diff --git a/src/google/adk/tools/agent_tool.py b/src/google/adk/tools/agent_tool.py
index 7a8b15b5..89086c90 100644
--- a/src/google/adk/tools/agent_tool.py
+++ b/src/google/adk/tools/agent_tool.py
@@ -135,7 +135,7 @@ class AgentTool(BaseTool):
     )
     session = await runner.session_service.create_session(
         app_name=self.agent.name,
-        user_id='tmp_user',
+        user_id=tool_context._invocation_context.user_id,
         state=tool_context.state.to_dict(),
     )