diff --git a/python/packages/autogen-core/src/autogen_core/memory/_base_memory.py b/python/packages/autogen-core/src/autogen_core/memory/_base_memory.py
index 577c23fda..5385b37d3 100644
--- a/python/packages/autogen-core/src/autogen_core/memory/_base_memory.py
+++ b/python/packages/autogen-core/src/autogen_core/memory/_base_memory.py
@@ -2,7 +2,7 @@ from abc import ABC, abstractmethod
 from enum import Enum
 from typing import Any, Dict, List, Union
 
-from pydantic import BaseModel, ConfigDict
+from pydantic import BaseModel, ConfigDict, field_serializer
 
 from .._cancellation_token import CancellationToken
 from .._component_config import ComponentBase
@@ -37,6 +37,13 @@ class MemoryContent(BaseModel):
 
     model_config = ConfigDict(arbitrary_types_allowed=True)
 
+    @field_serializer("mime_type")
+    def serialize_mime_type(self, mime_type: MemoryMimeType | str) -> str:
+        """Serialize the MIME type to a string."""
+        if isinstance(mime_type, MemoryMimeType):
+            return mime_type.value
+        return mime_type
+
 
 class MemoryQueryResult(BaseModel):
     """Result of a memory :meth:`~autogen_core.memory.Memory.query` operation."""