diff --git a/api/core/app/app_config/workflow_ui_based_app/variables/manager.py b/api/core/app/app_config/workflow_ui_based_app/variables/manager.py
index 13ace32fd6..c02a5aa3d8 100644
--- a/api/core/app/app_config/workflow_ui_based_app/variables/manager.py
+++ b/api/core/app/app_config/workflow_ui_based_app/variables/manager.py
@@ -1,4 +1,6 @@
+import json
 import re
+from typing import Any
 
 from core.app.app_config.entities import RagPipelineVariableEntity
 from graphon.variables.input_entities import VariableEntity
@@ -20,10 +22,32 @@ class WorkflowVariablesConfigManager:
 
         # variables
         for variable in user_input_form:
+            cls._normalize_json_schema(variable)
             variables.append(VariableEntity.model_validate(variable))
 
         return variables
 
+    @staticmethod
+    def _normalize_json_schema(variable: dict[str, Any]) -> None:
+        """
+        Normalize ``json_schema`` from a JSON string to a dict.
+
+        The workflow graph is stored as JSON in the database.  When a JSON
+        object variable carries a ``json_schema`` field, nested dicts are
+        preserved correctly, but older data or certain serialization paths
+        may store it as a JSON *string* instead of a native dict.
+
+        ``VariableEntity.json_schema`` expects ``dict | None``, so we
+        deserialize the string here before handing it to Pydantic.
+        """
+        json_schema = variable.get("json_schema")
+        if isinstance(json_schema, str):
+            try:
+                variable["json_schema"] = json.loads(json_schema)
+            except (json.JSONDecodeError, TypeError):
+                # Leave as-is; Pydantic validation will surface the error.
+                pass
+
     @classmethod
     def convert_rag_pipeline_variable(cls, workflow: Workflow, start_node_id: str) -> list[RagPipelineVariableEntity]:
         """
diff --git a/api/tests/unit_tests/core/app/app_config/workflow_ui_based_app/test_workflow_ui_based_app_manager.py b/api/tests/unit_tests/core/app/app_config/workflow_ui_based_app/test_workflow_ui_based_app_manager.py
index dacd69a578..e55109e296 100644
--- a/api/tests/unit_tests/core/app/app_config/workflow_ui_based_app/test_workflow_ui_based_app_manager.py
+++ b/api/tests/unit_tests/core/app/app_config/workflow_ui_based_app/test_workflow_ui_based_app_manager.py
@@ -74,6 +74,87 @@ class TestWorkflowVariablesConfigManagerConvert:
         with pytest.raises(ValueError):
             WorkflowVariablesConfigManager.convert(mock_workflow)
 
+    def test_convert_normalizes_json_schema_string_to_dict(self, mock_workflow, mock_variable_entity):
+        """Regression test for #36766: json_schema stored as a JSON string."""
+        import json
+
+        schema_dict = {"type": "object", "properties": {"name": {"type": "string"}}}
+        input_variables = [
+            {
+                "variable": "profile",
+                "label": "Profile",
+                "type": "json_object",
+                "json_schema": json.dumps(schema_dict),
+            }
+        ]
+        mock_workflow.user_input_form.return_value = input_variables
+        mock_variable_entity.model_validate.side_effect = lambda x: x
+
+        # Act
+        result = WorkflowVariablesConfigManager.convert(mock_workflow)
+
+        # Assert — the string was deserialized before reaching model_validate
+        assert result[0]["json_schema"] == schema_dict
+        assert isinstance(result[0]["json_schema"], dict)
+
+    def test_convert_normalizes_json_schema_dict_passthrough(self, mock_workflow, mock_variable_entity):
+        """json_schema already a dict should pass through unchanged."""
+        schema_dict = {"type": "object", "properties": {"age": {"type": "number"}}}
+        input_variables = [
+            {
+                "variable": "profile",
+                "label": "Profile",
+                "type": "json_object",
+                "json_schema": schema_dict,
+            }
+        ]
+        mock_workflow.user_input_form.return_value = input_variables
+        mock_variable_entity.model_validate.side_effect = lambda x: x
+
+        # Act
+        result = WorkflowVariablesConfigManager.convert(mock_workflow)
+
+        # Assert
+        assert result[0]["json_schema"] == schema_dict
+
+    def test_convert_normalizes_json_schema_none_passthrough(self, mock_workflow, mock_variable_entity):
+        """json_schema=None should pass through unchanged."""
+        input_variables = [
+            {
+                "variable": "name",
+                "label": "Name",
+                "type": "text-input",
+                "json_schema": None,
+            }
+        ]
+        mock_workflow.user_input_form.return_value = input_variables
+        mock_variable_entity.model_validate.side_effect = lambda x: x
+
+        # Act
+        result = WorkflowVariablesConfigManager.convert(mock_workflow)
+
+        # Assert
+        assert result[0]["json_schema"] is None
+
+    def test_convert_normalizes_json_schema_invalid_string_passthrough(self, mock_workflow, mock_variable_entity):
+        """Invalid JSON string should be left as-is for Pydantic to reject."""
+        input_variables = [
+            {
+                "variable": "profile",
+                "label": "Profile",
+                "type": "json_object",
+                "json_schema": "{invalid-json",
+            }
+        ]
+        mock_workflow.user_input_form.return_value = input_variables
+        mock_variable_entity.model_validate.side_effect = lambda x: x
+
+        # Act
+        result = WorkflowVariablesConfigManager.convert(mock_workflow)
+
+        # Assert — string left as-is
+        assert result[0]["json_schema"] == "{invalid-json"
+
 
 # =============================
 # Test convert_rag_pipeline_variable