diff --git a/api/controllers/console/auth/activate.py b/api/controllers/console/auth/activate.py
index 1f58dbe910f..3e9160f2bb0 100644
--- a/api/controllers/console/auth/activate.py
+++ b/api/controllers/console/auth/activate.py
@@ -7,10 +7,13 @@ from configs import dify_config
 from constants.languages import supported_language
 from controllers.common.schema import query_params_from_model, register_schema_models
 from controllers.console import console_ns
+from controllers.console.auth.error import InvitationAccountMismatchError
 from controllers.console.error import AccountInFreezeError, AlreadyActivateError
 from extensions.ext_database import db
 from libs.datetime_utils import naive_utc_now
 from libs.helper import EmailStr, timezone
+from libs.login import current_account_with_tenant
+from libs.token import extract_access_token
 from models import AccountStatus
 from models.account import TenantAccountJoin, TenantAccountRole
 from services.account_service import RegisterService, TenantService
@@ -136,6 +139,12 @@ class ActivateApi(Resource):
     )
     @console_ns.response(400, "Already activated or invalid token")
     def post(self):
+        """Accept an invitation without letting an existing session act for another account.
+
+        Token-only activation remains available for legacy clients. When the request already
+        carries a console session, that session must belong to the account encoded in the
+        invitation before the token is consumed or tenant membership is changed.
+        """
         args = ActivatePayload.model_validate(console_ns.payload)
 
         normalized_request_email = args.email.lower() if args.email else None
@@ -146,6 +155,11 @@ class ActivateApi(Resource):
             raise AlreadyActivateError()
 
         account = invitation["account"]
+        if extract_access_token(request):
+            current_account, _ = current_account_with_tenant()
+            if current_account.id != account.id:
+                raise InvitationAccountMismatchError()
+
         if dify_config.BILLING_ENABLED and BillingService.is_email_in_freeze(account.email):
             raise AccountInFreezeError()
 
diff --git a/api/controllers/console/auth/error.py b/api/controllers/console/auth/error.py
index 81f1c6e70fa..562de31270f 100644
--- a/api/controllers/console/auth/error.py
+++ b/api/controllers/console/auth/error.py
@@ -13,6 +13,12 @@ class InvalidEmailError(BaseHTTPException):
     code = 400
 
 
+class InvitationAccountMismatchError(BaseHTTPException):
+    error_code = "invitation_account_mismatch"
+    description = "This invitation was sent to another account. Please sign in with the invited account."
+    code = 403
+
+
 class PasswordMismatchError(BaseHTTPException):
     error_code = "password_mismatch"
     description = "The passwords do not match."
diff --git a/api/openapi/markdown/console-openapi.md b/api/openapi/markdown/console-openapi.md
index 22496868c8c..15562e91955 100644
--- a/api/openapi/markdown/console-openapi.md
+++ b/api/openapi/markdown/console-openapi.md
@@ -260,7 +260,12 @@ Get account avatar url
 | 200 | Success | **application/json**: [AccountResponse](#accountresponse)<br> |
 
 ### [POST] /activate
+**Accept an invitation without letting an existing session act for another account**
+
 Activate account with invitation token
+Token-only activation remains available for legacy clients. When the request already
+carries a console session, that session must belong to the account encoded in the
+invitation before the token is consumed or tenant membership is changed.
 
 #### Request Body
 
diff --git a/api/tests/unit_tests/controllers/console/auth/test_account_activation.py b/api/tests/unit_tests/controllers/console/auth/test_account_activation.py
index 001ca0bf8fb..7669eed8d2a 100644
--- a/api/tests/unit_tests/controllers/console/auth/test_account_activation.py
+++ b/api/tests/unit_tests/controllers/console/auth/test_account_activation.py
@@ -14,6 +14,7 @@ import pytest
 from flask import Flask
 
 from controllers.console.auth.activate import ActivateApi, ActivateCheckApi
+from controllers.console.auth.error import InvitationAccountMismatchError
 from controllers.console.error import AccountInFreezeError, AlreadyActivateError
 from models.account import AccountStatus, TenantAccountRole
 
@@ -202,6 +203,50 @@ class TestActivateApi:
         with patch("controllers.console.auth.activate.TenantService.switch_tenant") as mock:
             yield mock
 
+    @patch("controllers.console.auth.activate.TenantService.create_tenant_member")
+    @patch("controllers.console.auth.activate.RegisterService.get_invitation_with_case_fallback")
+    @patch("controllers.console.auth.activate.RegisterService.revoke_token")
+    @patch("controllers.console.auth.activate.current_account_with_tenant")
+    @patch("controllers.console.auth.activate.extract_access_token", return_value="access-token")
+    @patch("controllers.console.auth.activate.db")
+    def test_activation_rejects_invitation_for_different_authenticated_account(
+        self,
+        mock_db: MagicMock,
+        mock_extract_access_token: MagicMock,
+        mock_current_account_with_tenant: MagicMock,
+        mock_revoke_token: MagicMock,
+        mock_get_invitation: MagicMock,
+        mock_create_tenant_member: MagicMock,
+        app: Flask,
+        mock_invitation: MagicMock,
+        mock_account: MagicMock,
+        mock_switch_tenant: MagicMock,
+    ):
+        """A logged-in account cannot consume another account's invitation token."""
+        current_account = MagicMock()
+        current_account.id = "current-account-id"
+        mock_account.id = "invited-account-id"
+        mock_account.status = AccountStatus.ACTIVE
+        mock_invitation["data"]["requires_setup"] = False
+        mock_get_invitation.return_value = mock_invitation
+        mock_current_account_with_tenant.return_value = (current_account, "current-workspace-id")
+
+        with app.test_request_context(
+            "/activate",
+            method="POST",
+            json={
+                "token": "valid_token",
+            },
+        ):
+            with pytest.raises(InvitationAccountMismatchError):
+                ActivateApi().post()
+
+        mock_extract_access_token.assert_called_once()
+        mock_revoke_token.assert_not_called()
+        mock_create_tenant_member.assert_not_called()
+        mock_switch_tenant.assert_not_called()
+        mock_db.session.scalar.assert_not_called()
+
     @patch("controllers.console.auth.activate.RegisterService.get_invitation_if_token_valid")
     @patch("controllers.console.auth.activate.RegisterService.revoke_token")
     @patch("controllers.console.auth.activate.db")
diff --git a/packages/contracts/generated/api/console/activate/orpc.gen.ts b/packages/contracts/generated/api/console/activate/orpc.gen.ts
index 5ab609f5bb9..3bb61c9e7f1 100644
--- a/packages/contracts/generated/api/console/activate/orpc.gen.ts
+++ b/packages/contracts/generated/api/console/activate/orpc.gen.ts
@@ -29,15 +29,22 @@ export const check = {
 }
 
 /**
+ * Accept an invitation without letting an existing session act for another account
+ *
  * Activate account with invitation token
+ * Token-only activation remains available for legacy clients. When the request already
+ * carries a console session, that session must belong to the account encoded in the
+ * invitation before the token is consumed or tenant membership is changed.
  */
 export const post = oc
   .route({
-    description: 'Activate account with invitation token',
+    description:
+      'Activate account with invitation token\nToken-only activation remains available for legacy clients. When the request already\ncarries a console session, that session must belong to the account encoded in the\ninvitation before the token is consumed or tenant membership is changed.',
     inputStructure: 'detailed',
     method: 'POST',
     operationId: 'postActivate',
     path: '/activate',
+    summary: 'Accept an invitation without letting an existing session act for another account',
     tags: ['console'],
   })
   .input(z.object({ body: zPostActivateBody }))
diff --git a/web/app/signin/__tests__/normal-form.spec.tsx b/web/app/signin/__tests__/normal-form.spec.tsx
index a5e39601b29..5bbb2eb6529 100644
--- a/web/app/signin/__tests__/normal-form.spec.tsx
+++ b/web/app/signin/__tests__/normal-form.spec.tsx
@@ -53,6 +53,7 @@ const loggedInQueryResult = {
   data: {
     profile: {
       id: 'account-id',
+      email: 'invitee@example.com',
     },
   },
   error: null,
@@ -77,6 +78,16 @@ const nonInviteQueryResult = {
   data: undefined,
 }
 
+const mockQueryResults = (
+  profileResult: ReturnType<typeof useQuery>,
+  inviteResult: ReturnType<typeof useQuery>,
+) => {
+  mockUseQuery.mockImplementation((options) => {
+    const queryKey = options.queryKey as readonly unknown[]
+    return (queryKey[0] === 'account' ? profileResult : inviteResult) as ReturnType<typeof useQuery>
+  })
+}
+
 describe('NormalForm', () => {
   beforeEach(() => {
     vi.clearAllMocks()
@@ -104,9 +115,10 @@ describe('NormalForm', () => {
     it('should send logged-in visitors without a redirect target to the console home', async () => {
       const searchParams = new URLSearchParams()
       mockUseSearchParams.mockReturnValue(searchParams)
-      mockUseQuery
-        .mockReturnValueOnce(loggedInQueryResult as unknown as ReturnType<typeof useQuery>)
-        .mockReturnValueOnce(nonInviteQueryResult as unknown as ReturnType<typeof useQuery>)
+      mockQueryResults(
+        loggedInQueryResult as unknown as ReturnType<typeof useQuery>,
+        nonInviteQueryResult as unknown as ReturnType<typeof useQuery>,
+      )
 
       render(<NormalForm />)
 
@@ -119,9 +131,10 @@ describe('NormalForm', () => {
       mockUseSearchParams.mockReturnValue(
         new URLSearchParams('redirect_url=https%3A%2F%2Fgoogle.com'),
       )
-      mockUseQuery
-        .mockReturnValueOnce(loggedInQueryResult as unknown as ReturnType<typeof useQuery>)
-        .mockReturnValueOnce(nonInviteQueryResult as unknown as ReturnType<typeof useQuery>)
+      mockQueryResults(
+        loggedInQueryResult as unknown as ReturnType<typeof useQuery>,
+        nonInviteQueryResult as unknown as ReturnType<typeof useQuery>,
+      )
 
       render(<NormalForm />)
 
@@ -134,9 +147,60 @@ describe('NormalForm', () => {
   describe('Invite Redirects', () => {
     it('should send logged-in invite visitors to the invite confirmation page', async () => {
       mockUseSearchParams.mockReturnValue(new URLSearchParams('invite_token=invite-token'))
-      mockUseQuery
-        .mockReturnValueOnce(loggedInQueryResult as unknown as ReturnType<typeof useQuery>)
-        .mockReturnValueOnce(invitationQueryResult as unknown as ReturnType<typeof useQuery>)
+      mockQueryResults(
+        loggedInQueryResult as unknown as ReturnType<typeof useQuery>,
+        invitationQueryResult as unknown as ReturnType<typeof useQuery>,
+      )
+
+      render(<NormalForm />)
+
+      await waitFor(() => {
+        expect(mockReplace).toHaveBeenCalledWith(
+          '/signin/invite-settings?invite_token=invite-token',
+        )
+      })
+    })
+
+    it('should keep a different logged-in account on the invitation sign-in form', () => {
+      mockUseSearchParams.mockReturnValue(new URLSearchParams('invite_token=invite-token'))
+      mockQueryResults(
+        {
+          ...loggedInQueryResult,
+          data: {
+            profile: {
+              id: 'account-id',
+              email: 'current@example.com',
+            },
+          },
+        } as unknown as ReturnType<typeof useQuery>,
+        invitationQueryResult as unknown as ReturnType<typeof useQuery>,
+      )
+
+      const queryClient = new QueryClient()
+      render(
+        <QueryClientProvider client={queryClient}>
+          <NormalForm />
+        </QueryClientProvider>,
+      )
+
+      expect(screen.getByRole('button', { name: 'login.signBtn' })).toBeInTheDocument()
+      expect(mockReplace).not.toHaveBeenCalled()
+    })
+
+    it('should match the logged-in account email case-insensitively', async () => {
+      mockUseSearchParams.mockReturnValue(new URLSearchParams('invite_token=invite-token'))
+      mockQueryResults(
+        {
+          ...loggedInQueryResult,
+          data: {
+            profile: {
+              id: 'account-id',
+              email: 'Invitee@Example.com',
+            },
+          },
+        } as unknown as ReturnType<typeof useQuery>,
+        invitationQueryResult as unknown as ReturnType<typeof useQuery>,
+      )
 
       render(<NormalForm />)
 
@@ -153,7 +217,10 @@ describe('NormalForm', () => {
       mockUseSearchParams.mockReturnValue(
         new URLSearchParams('redirect_url=%2Fapps%3Ftag%3Dworkflow&source=pricing'),
       )
-      mockUseQuery.mockReturnValue(nonInviteQueryResult as unknown as ReturnType<typeof useQuery>)
+      mockQueryResults(
+        nonInviteQueryResult as unknown as ReturnType<typeof useQuery>,
+        nonInviteQueryResult as unknown as ReturnType<typeof useQuery>,
+      )
       mockUseSuspenseQuery.mockReturnValue({
         data: {
           enable_social_oauth_login: false,
diff --git a/web/app/signin/invite-settings/__tests__/page.spec.tsx b/web/app/signin/invite-settings/__tests__/page.spec.tsx
index f76974a11fa..907f95893a5 100644
--- a/web/app/signin/invite-settings/__tests__/page.spec.tsx
+++ b/web/app/signin/invite-settings/__tests__/page.spec.tsx
@@ -1,4 +1,5 @@
 import type { MockedFunction } from 'vitest'
+import { useQuery } from '@tanstack/react-query'
 import { fireEvent, render, screen, waitFor } from '@testing-library/react'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 import { useLocale } from '@/context/i18n'
@@ -13,6 +14,7 @@ vi.mock('@tanstack/react-query', async () => {
     await vi.importActual<typeof import('@tanstack/react-query')>('@tanstack/react-query')
   return {
     ...actual,
+    useQuery: vi.fn(),
     useQueryClient: vi.fn(() => ({
       resetQueries: vi.fn(),
     })),
@@ -65,6 +67,7 @@ const mockUseLocale = useLocale as unknown as MockedFunction<typeof useLocale>
 const mockUseRouter = useRouter as unknown as MockedFunction<typeof useRouter>
 const mockUseSearchParams = useSearchParams as unknown as MockedFunction<typeof useSearchParams>
 const mockActivateMember = activateMember as unknown as MockedFunction<typeof activateMember>
+const mockUseQuery = vi.mocked(useQuery)
 const mockUseInvitationCheck = useInvitationCheck as unknown as MockedFunction<
   typeof useInvitationCheck
 >
@@ -96,6 +99,16 @@ describe('InviteSettingsPage', () => {
       },
       refetch: mockRefetch,
     } as unknown as ReturnType<typeof useInvitationCheck>)
+    mockUseQuery.mockReturnValue({
+      data: {
+        profile: {
+          id: 'account-id',
+          email: 'invitee@example.com',
+        },
+      },
+      isPending: false,
+      error: null,
+    } as unknown as ReturnType<typeof useQuery>)
     mockGetBrowserTimezone.mockReturnValue('Asia/Shanghai')
     mockActivateMember.mockResolvedValue({ result: 'success' })
   })
@@ -260,4 +273,45 @@ describe('InviteSettingsPage', () => {
       })
     })
   })
+
+  describe('Invitation account guard', () => {
+    it('should redirect a different logged-in account back to the invitation sign-in form', async () => {
+      mockUseQuery.mockReturnValue({
+        data: {
+          profile: {
+            id: 'current-account-id',
+            email: 'current@example.com',
+          },
+        },
+        isPending: false,
+        error: null,
+      } as unknown as ReturnType<typeof useQuery>)
+
+      render(<InviteSettingsPage />)
+
+      await waitFor(() => {
+        expect(mockReplace).toHaveBeenCalledWith('/signin?invite_token=invite-token')
+      })
+      expect(screen.queryByRole('button', { name: 'login.join Acme' })).not.toBeInTheDocument()
+      expect(mockActivateMember).not.toHaveBeenCalled()
+    })
+
+    it('should allow case-insensitive email matches', () => {
+      mockUseQuery.mockReturnValue({
+        data: {
+          profile: {
+            id: 'account-id',
+            email: 'Invitee@Example.com',
+          },
+        },
+        isPending: false,
+        error: null,
+      } as unknown as ReturnType<typeof useQuery>)
+
+      render(<InviteSettingsPage />)
+
+      expect(screen.getByRole('button', { name: 'login.join Acme' })).toBeInTheDocument()
+      expect(mockReplace).not.toHaveBeenCalled()
+    })
+  })
 })
diff --git a/web/app/signin/invite-settings/page.tsx b/web/app/signin/invite-settings/page.tsx
index 41de03fa7b4..33eeea9e6c2 100644
--- a/web/app/signin/invite-settings/page.tsx
+++ b/web/app/signin/invite-settings/page.tsx
@@ -12,13 +12,14 @@ import {
 } from '@langgenius/dify-ui/select'
 import { toast } from '@langgenius/dify-ui/toast'
 import { RiAccountCircleLine } from '@remixicon/react'
-import { useQueryClient, useSuspenseQuery } from '@tanstack/react-query'
+import { useQuery, useQueryClient, useSuspenseQuery } from '@tanstack/react-query'
 import { noop } from 'es-toolkit/function'
-import { useCallback, useState } from 'react'
+import { useCallback, useEffect, useState } from 'react'
 import { useTranslation } from 'react-i18next'
 import Loading from '@/app/components/base/loading'
 import { LICENSE_LINK } from '@/constants/link'
 import { useLocale } from '@/context/i18n'
+import { isLegacyBase401, userProfileQueryOptions } from '@/features/account-profile/client'
 import { systemFeaturesQueryOptions } from '@/features/system-features/client'
 import { i18n, setLocaleOnClient } from '@/i18n-config'
 import { languages } from '@/i18n-config/language'
@@ -30,6 +31,7 @@ import { useInvitationCheck } from '@/service/use-common'
 import { replaceLoginRedirect } from '@/utils/login-redirect.client'
 import { getBrowserTimezone, timezones } from '@/utils/timezone'
 import { basePath } from '@/utils/var'
+import { isInvitationForAccount } from '../utils/invitation-account'
 import { resolvePostLoginRedirect } from '../utils/post-login-redirect'
 
 type LanguageSelectOption = {
@@ -67,6 +69,15 @@ export default function InviteSettingsPage() {
   const queryClient = useQueryClient()
   const searchParams = useSearchParams()
   const token = decodeURIComponent(searchParams.get('invite_token') as string)
+  const {
+    data: userResp,
+    isPending: isProfilePending,
+    error: profileError,
+  } = useQuery({
+    ...userProfileQueryOptions(),
+    throwOnError: (err) => !isLegacyBase401(err),
+    refetchOnWindowFocus: false,
+  })
   const locale = useLocale()
   const [name, setName] = useState('')
   const [isActivating, setIsActivating] = useState(false)
@@ -92,11 +103,28 @@ export default function InviteSettingsPage() {
     },
   }
   const { data: checkRes, refetch: recheck } = useInvitationCheck(checkParams.params, !!token)
+  const isInvitationForCurrentAccount = isInvitationForAccount(
+    checkRes?.data?.email,
+    userResp?.profile.email,
+  )
+  const shouldReturnToSignIn =
+    !isProfilePending &&
+    Boolean(
+      checkRes?.is_valid &&
+      (isLegacyBase401(profileError) || (userResp && !isInvitationForCurrentAccount)),
+    )
   const requiresAccountSetup =
     checkRes?.data?.requires_setup ?? checkRes?.data?.account_status === 'pending'
 
+  useEffect(() => {
+    if (!shouldReturnToSignIn) return
+
+    router.replace(`/signin?${searchParams.toString()}`)
+  }, [router, searchParams, shouldReturnToSignIn])
+
   const handleActivate = useCallback(async () => {
     try {
+      if (!isInvitationForCurrentAccount) return
       if (requiresAccountSetup && !name) {
         toast.error(t(($) => $.enterYourName, { ns: 'login' }))
         return
@@ -127,7 +155,7 @@ export default function InviteSettingsPage() {
       setIsActivating(false)
     }
   }, [
-    isActivating,
+    isInvitationForCurrentAccount,
     language,
     name,
     queryClient,
@@ -140,7 +168,7 @@ export default function InviteSettingsPage() {
     t,
   ])
 
-  if (!checkRes) return <Loading />
+  if (isProfilePending || shouldReturnToSignIn || !checkRes) return <Loading />
   if (!checkRes.is_valid) {
     return (
       <div className="flex flex-col md:w-[400px]">
diff --git a/web/app/signin/normal-form.tsx b/web/app/signin/normal-form.tsx
index 008f781d7b8..6604d1d8786 100644
--- a/web/app/signin/normal-form.tsx
+++ b/web/app/signin/normal-form.tsx
@@ -19,6 +19,7 @@ import MailAndPasswordAuth from './components/mail-and-password-auth'
 import SocialAuth from './components/social-auth'
 import SSOAuth from './components/sso-auth'
 import Split from './split'
+import { isInvitationForAccount } from './utils/invitation-account'
 import { resolvePostLoginRedirect } from './utils/post-login-redirect'
 
 type AuthType = 'code' | 'password'
@@ -67,6 +68,10 @@ function NormalForm() {
   })
 
   const workspaceName = invitationCheckResp?.data?.workspace_name || ''
+  const isInvitationForCurrentAccount = isInvitationForAccount(
+    invitationCheckResp?.data?.email,
+    userResp?.profile.email,
+  )
   const hasSocialLogin = systemFeatures.enable_social_oauth_login
   const hasSsoLogin = Boolean(systemFeatures.sso_enforced_for_signin)
   const hasEmailCodeLogin = systemFeatures.enable_email_code_login
@@ -83,18 +88,21 @@ function NormalForm() {
   const noLoginMethodsConfigured =
     !hasSocialLogin && !hasEmailCodeLogin && !hasEmailPasswordLogin && !hasSsoLogin
   const allMethodsAreDisabled = noLoginMethodsConfigured || isInviteCheckError
-  const isLoading = isCheckLoading || isLoggedIn || (isInviteLink && isInviteCheckLoading)
+  const shouldRedirectLoggedInUser = isLoggedIn && (!isInviteLink || isInvitationForCurrentAccount)
+  const isLoading =
+    isCheckLoading || shouldRedirectLoggedInUser || (isInviteLink && isInviteCheckLoading)
 
   useEffect(() => {
     if (!isLoggedIn) return
 
     if (isInviteLink) {
+      if (!isInvitationForCurrentAccount) return
       router.replace(`/signin/invite-settings?${searchParams.toString()}`)
       return
     }
 
     replaceLoginRedirect(resolvePostLoginRedirect(searchParams), router.replace, basePath)
-  }, [isInviteLink, isLoggedIn, router, searchParams])
+  }, [isInvitationForCurrentAccount, isInviteLink, isLoggedIn, router, searchParams])
 
   useEffect(() => {
     if (message) toast.error(message)
diff --git a/web/app/signin/utils/invitation-account.ts b/web/app/signin/utils/invitation-account.ts
new file mode 100644
index 00000000000..a5ae0a0ff95
--- /dev/null
+++ b/web/app/signin/utils/invitation-account.ts
@@ -0,0 +1,9 @@
+export const isInvitationForAccount = (
+  invitationEmail?: string | null,
+  accountEmail?: string | null,
+) =>
+  Boolean(
+    invitationEmail &&
+    accountEmail &&
+    invitationEmail.trim().toLowerCase() === accountEmail.trim().toLowerCase(),
+  )