diff --git a/src/google/adk/tools/mcp_tool/mcp_session_manager.py b/src/google/adk/tools/mcp_tool/mcp_session_manager.py
index fbe843a510..0f75078b15 100644
--- a/src/google/adk/tools/mcp_tool/mcp_session_manager.py
+++ b/src/google/adk/tools/mcp_tool/mcp_session_manager.py
@@ -25,17 +25,22 @@
 from typing import Any
 from typing import Dict
 from typing import Optional
+from typing import Protocol
+from typing import runtime_checkable
 from typing import TextIO
 from typing import Union
 
 import anyio
 from pydantic import BaseModel
+from pydantic import ConfigDict
 
 try:
   from mcp import ClientSession
   from mcp import StdioServerParameters
   from mcp.client.sse import sse_client
   from mcp.client.stdio import stdio_client
+  from mcp.client.streamable_http import create_mcp_http_client
+  from mcp.client.streamable_http import McpHttpClientFactory
   from mcp.client.streamable_http import streamablehttp_client
 except ImportError as e:
 
@@ -84,6 +89,11 @@ class SseConnectionParams(BaseModel):
   sse_read_timeout: float = 60 * 5.0
 
 
+@runtime_checkable
+class CheckableMcpHttpClientFactory(McpHttpClientFactory, Protocol):
+  pass
+
+
 class StreamableHTTPConnectionParams(BaseModel):
   """Parameters for the MCP Streamable HTTP connection.
 
@@ -99,13 +109,18 @@ class StreamableHTTPConnectionParams(BaseModel):
         Streamable HTTP server.
       terminate_on_close: Whether to terminate the MCP Streamable HTTP server
         when the connection is closed.
+      httpx_client_factory: Factory function to create a custom HTTPX client. If
+        not provided, a default factory will be used.
   """
 
+  model_config = ConfigDict(arbitrary_types_allowed=True)
+
   url: str
   headers: dict[str, Any] | None = None
   timeout: float = 5.0
   sse_read_timeout: float = 60 * 5.0
   terminate_on_close: bool = True
+  httpx_client_factory: CheckableMcpHttpClientFactory = create_mcp_http_client
 
 
 def retry_on_closed_resource(func):
@@ -285,6 +300,7 @@ def _create_client(self, merged_headers: Optional[Dict[str, str]] = None):
               seconds=self._connection_params.sse_read_timeout
           ),
           terminate_on_close=self._connection_params.terminate_on_close,
+          httpx_client_factory=self._connection_params.httpx_client_factory,
       )
     else:
       raise ValueError(
diff --git a/tests/unittests/tools/mcp_tool/test_mcp_session_manager.py b/tests/unittests/tools/mcp_tool/test_mcp_session_manager.py
index 559e51719a..5b827fb170 100644
--- a/tests/unittests/tools/mcp_tool/test_mcp_session_manager.py
+++ b/tests/unittests/tools/mcp_tool/test_mcp_session_manager.py
@@ -144,6 +144,59 @@ def test_init_with_streamable_http_params(self):
 
     assert manager._connection_params == http_params
 
+  @patch("google.adk.tools.mcp_tool.mcp_session_manager.streamablehttp_client")
+  def test_init_with_streamable_http_custom_httpx_factory(
+      self, mock_streamablehttp_client
+  ):
+    """Test that streamablehttp_client is called with custom httpx_client_factory."""
+    from datetime import timedelta
+
+    custom_httpx_factory = Mock()
+
+    http_params = StreamableHTTPConnectionParams(
+        url="https://example.com/mcp",
+        timeout=15.0,
+        httpx_client_factory=custom_httpx_factory,
+    )
+    manager = MCPSessionManager(http_params)
+
+    manager._create_client()
+
+    mock_streamablehttp_client.assert_called_once_with(
+        url="https://example.com/mcp",
+        headers=None,
+        timeout=timedelta(seconds=15.0),
+        sse_read_timeout=timedelta(seconds=300.0),
+        terminate_on_close=True,
+        httpx_client_factory=custom_httpx_factory,
+    )
+
+  @pytest.mark.asyncio
+  @patch("google.adk.tools.mcp_tool.mcp_session_manager.streamablehttp_client")
+  async def test_init_with_streamable_http_default_httpx_factory(
+      self, mock_streamablehttp_client
+  ):
+    """Test that streamablehttp_client is called with custom httpx_client_factory."""
+    from datetime import timedelta
+
+    from mcp.client.streamable_http import create_mcp_http_client
+
+    http_params = StreamableHTTPConnectionParams(
+        url="https://example.com/mcp", timeout=15.0
+    )
+    manager = MCPSessionManager(http_params)
+
+    manager._create_client()
+
+    mock_streamablehttp_client.assert_called_once_with(
+        url="https://example.com/mcp",
+        headers=None,
+        timeout=timedelta(seconds=15.0),
+        sse_read_timeout=timedelta(seconds=300.0),
+        terminate_on_close=True,
+        httpx_client_factory=create_mcp_http_client,
+    )
+
   def test_generate_session_key_stdio(self):
     """Test session key generation for stdio connections."""
     manager = MCPSessionManager(self.mock_stdio_connection_params)