diff --git a/api/controllers/service_api/app/completion.py b/api/controllers/service_api/app/completion.py
index bbacf076c7..21c289ca82 100644
--- a/api/controllers/service_api/app/completion.py
+++ b/api/controllers/service_api/app/completion.py
@@ -8,6 +8,7 @@ from pydantic import BaseModel, Field, ValidationInfo, field_validator
 from werkzeug.exceptions import BadRequest, InternalServerError, NotFound
 
 import services
+from constants import UUID_NIL
 from controllers.common.schema import register_schema_models
 from controllers.service_api import service_api_ns
 from controllers.service_api.app.error import (
@@ -87,7 +88,7 @@ def _validate_parent_message_request(
     conversation_id: str | None,
     parent_message_id: str | None,
 ) -> None:
-    if not parent_message_id:
+    if not parent_message_id or parent_message_id == UUID_NIL:
         return
 
     if not conversation_id:
diff --git a/api/core/app/apps/advanced_chat/app_generator.py b/api/core/app/apps/advanced_chat/app_generator.py
index 452d0efb67..88255bdb53 100644
--- a/api/core/app/apps/advanced_chat/app_generator.py
+++ b/api/core/app/apps/advanced_chat/app_generator.py
@@ -126,6 +126,14 @@ class AdvancedChatAppGenerator(MessageBasedAppGenerator):
                 app_model=app_model, conversation_id=conversation_id, user=user
             )
 
+        self._validate_parent_message_for_service_api(
+            app_model=app_model,
+            user=user,
+            conversation=conversation,
+            parent_message_id=args.get("parent_message_id"),
+            invoke_from=invoke_from,
+        )
+
         # parse files
         # TODO(QuantumGhost): Move file parsing logic to the API controller layer
         # for better separation of concerns.
diff --git a/api/core/app/apps/agent_chat/app_generator.py b/api/core/app/apps/agent_chat/app_generator.py
index 8af412add4..38b261a17a 100644
--- a/api/core/app/apps/agent_chat/app_generator.py
+++ b/api/core/app/apps/agent_chat/app_generator.py
@@ -104,6 +104,14 @@ class AgentChatAppGenerator(MessageBasedAppGenerator):
             conversation = ConversationService.get_conversation(
                 app_model=app_model, conversation_id=conversation_id, user=user
             )
+
+        self._validate_parent_message_for_service_api(
+            app_model=app_model,
+            user=user,
+            conversation=conversation,
+            parent_message_id=args.get("parent_message_id"),
+            invoke_from=invoke_from,
+        )
         # get app model config
         app_model_config = self._get_app_model_config(app_model=app_model, conversation=conversation)
 
diff --git a/api/core/app/apps/chat/app_generator.py b/api/core/app/apps/chat/app_generator.py
index a94fe1731f..fb24e87826 100644
--- a/api/core/app/apps/chat/app_generator.py
+++ b/api/core/app/apps/chat/app_generator.py
@@ -96,6 +96,14 @@ class ChatAppGenerator(MessageBasedAppGenerator):
             conversation = ConversationService.get_conversation(
                 app_model=app_model, conversation_id=conversation_id, user=user
             )
+
+        self._validate_parent_message_for_service_api(
+            app_model=app_model,
+            user=user,
+            conversation=conversation,
+            parent_message_id=args.get("parent_message_id"),
+            invoke_from=invoke_from,
+        )
         # get app model config
         app_model_config = self._get_app_model_config(app_model=app_model, conversation=conversation)
 
diff --git a/api/core/app/apps/message_based_app_generator.py b/api/core/app/apps/message_based_app_generator.py
index 3a00c08152..d58ff3a67c 100644
--- a/api/core/app/apps/message_based_app_generator.py
+++ b/api/core/app/apps/message_based_app_generator.py
@@ -35,6 +35,7 @@ from models.model import App, AppMode, AppModelConfig, Conversation, EndUser, Me
 from services.errors.app_model_config import AppModelConfigBrokenError
 from services.errors.conversation import ConversationNotExistsError
 from services.errors.message import MessageNotExistsError
+from services.message_service import MessageService
 
 logger = logging.getLogger(__name__)
 
@@ -91,6 +92,28 @@ class MessageBasedAppGenerator(BaseAppGenerator):
             return UUID_NIL
         return parent_message_id
 
+    def _validate_parent_message_for_service_api(
+        self,
+        *,
+        app_model: App,
+        user: Union[Account, EndUser],
+        conversation: Conversation | None,
+        parent_message_id: str | None,
+        invoke_from: InvokeFrom,
+    ) -> None:
+        if invoke_from != InvokeFrom.SERVICE_API:
+            return
+
+        if not parent_message_id or parent_message_id == UUID_NIL:
+            return
+
+        if not conversation:
+            raise ConversationNotExistsError("Conversation not exists")
+
+        parent_message = MessageService.get_message(app_model=app_model, user=user, message_id=parent_message_id)
+        if parent_message.conversation_id != conversation.id:
+            raise MessageNotExistsError("Message not exists")
+
     def _get_app_model_config(self, app_model: App, conversation: Conversation | None = None) -> AppModelConfig:
         if conversation:
             stmt = select(AppModelConfig).where(
diff --git a/api/tests/unit_tests/controllers/service_api/app/test_chat_parent_message_validation.py b/api/tests/unit_tests/controllers/service_api/app/test_chat_parent_message_validation.py
index 808d0c6a18..dde0bb08ed 100644
--- a/api/tests/unit_tests/controllers/service_api/app/test_chat_parent_message_validation.py
+++ b/api/tests/unit_tests/controllers/service_api/app/test_chat_parent_message_validation.py
@@ -4,6 +4,7 @@ from unittest.mock import patch
 import pytest
 from werkzeug.exceptions import BadRequest, NotFound
 
+from constants import UUID_NIL
 from controllers.service_api.app.completion import _validate_parent_message_request
 from services.errors.conversation import ConversationNotExistsError
 from services.errors.message import MessageNotExistsError
@@ -25,6 +26,25 @@ def test_validate_parent_message_skips_when_missing():
         get_message.assert_not_called()
 
 
+def test_validate_parent_message_skips_uuid_nil():
+    app_model = object()
+    end_user = object()
+
+    with (
+        patch("controllers.service_api.app.completion.ConversationService.get_conversation") as get_conversation,
+        patch("controllers.service_api.app.completion.MessageService.get_message") as get_message,
+    ):
+        _validate_parent_message_request(
+            app_model=app_model,
+            end_user=end_user,
+            conversation_id=None,
+            parent_message_id=UUID_NIL,
+        )
+
+        get_conversation.assert_not_called()
+        get_message.assert_not_called()
+
+
 def test_validate_parent_message_requires_conversation_id():
     app_model = object()
     end_user = object()
diff --git a/api/tests/unit_tests/core/app/apps/test_message_based_app_generator_parent_message.py b/api/tests/unit_tests/core/app/apps/test_message_based_app_generator_parent_message.py
new file mode 100644
index 0000000000..3cb7a0f62a
--- /dev/null
+++ b/api/tests/unit_tests/core/app/apps/test_message_based_app_generator_parent_message.py
@@ -0,0 +1,90 @@
+from types import SimpleNamespace
+from unittest.mock import patch
+
+import pytest
+
+from constants import UUID_NIL
+from core.app.apps.message_based_app_generator import MessageBasedAppGenerator
+from core.app.entities.app_invoke_entities import InvokeFrom
+from services.errors.conversation import ConversationNotExistsError
+from services.errors.message import MessageNotExistsError
+
+
+def test_validate_parent_message_service_api_skips_missing():
+    generator = MessageBasedAppGenerator()
+
+    with patch("core.app.apps.message_based_app_generator.MessageService.get_message") as get_message:
+        generator._validate_parent_message_for_service_api(
+            app_model=object(),
+            user=object(),
+            conversation=None,
+            parent_message_id=None,
+            invoke_from=InvokeFrom.SERVICE_API,
+        )
+
+        get_message.assert_not_called()
+
+
+def test_validate_parent_message_service_api_skips_uuid_nil():
+    generator = MessageBasedAppGenerator()
+
+    with patch("core.app.apps.message_based_app_generator.MessageService.get_message") as get_message:
+        generator._validate_parent_message_for_service_api(
+            app_model=object(),
+            user=object(),
+            conversation=None,
+            parent_message_id=UUID_NIL,
+            invoke_from=InvokeFrom.SERVICE_API,
+        )
+
+        get_message.assert_not_called()
+
+
+def test_validate_parent_message_service_api_requires_conversation():
+    generator = MessageBasedAppGenerator()
+
+    with pytest.raises(ConversationNotExistsError):
+        generator._validate_parent_message_for_service_api(
+            app_model=object(),
+            user=object(),
+            conversation=None,
+            parent_message_id="parent-id",
+            invoke_from=InvokeFrom.SERVICE_API,
+        )
+
+
+def test_validate_parent_message_service_api_mismatch_conversation():
+    generator = MessageBasedAppGenerator()
+    conversation = SimpleNamespace(id="conversation-id")
+    parent_message = SimpleNamespace(conversation_id="different-id")
+
+    with patch(
+        "core.app.apps.message_based_app_generator.MessageService.get_message",
+        return_value=parent_message,
+    ):
+        with pytest.raises(MessageNotExistsError):
+            generator._validate_parent_message_for_service_api(
+                app_model=object(),
+                user=object(),
+                conversation=conversation,
+                parent_message_id="parent-id",
+                invoke_from=InvokeFrom.SERVICE_API,
+            )
+
+
+def test_validate_parent_message_service_api_matches_conversation():
+    generator = MessageBasedAppGenerator()
+    conversation = SimpleNamespace(id="conversation-id")
+    parent_message = SimpleNamespace(conversation_id="conversation-id")
+
+    with patch(
+        "core.app.apps.message_based_app_generator.MessageService.get_message",
+        return_value=parent_message,
+    ):
+        generator._validate_parent_message_for_service_api(
+            app_model=object(),
+            user=object(),
+            conversation=conversation,
+            parent_message_id="parent-id",
+            invoke_from=InvokeFrom.SERVICE_API,
+        )