diff --git a/src/google/adk/integrations/firestore/firestore_session_service.py b/src/google/adk/integrations/firestore/firestore_session_service.py
index 83b97c33c2..4096dfcdf3 100644
--- a/src/google/adk/integrations/firestore/firestore_session_service.py
+++ b/src/google/adk/integrations/firestore/firestore_session_service.py
@@ -410,6 +410,16 @@ async def list_sessions(
         s_state = data.get("state", {})
         u_state = user_states_map.get(u_id, {})
         merged = self._merge_state(app_state, u_state, s_state)
+        update_time = data.get("updateTime")
+        last_update_time = 0.0
+        if update_time:
+          if isinstance(update_time, datetime):
+            last_update_time = update_time.timestamp()
+          else:
+            try:
+              last_update_time = float(update_time)
+            except (ValueError, TypeError):
+              pass
 
         sessions.append(
             Session(
@@ -418,7 +428,7 @@ async def list_sessions(
                 user_id=data["userId"],
                 state=merged,
                 events=[],
-                last_update_time=0.0,
+                last_update_time=last_update_time,
             )
         )
 
diff --git a/tests/unittests/integrations/firestore/test_firestore_session_service.py b/tests/unittests/integrations/firestore/test_firestore_session_service.py
index 1445bfe0ef..ecfb40b63b 100644
--- a/tests/unittests/integrations/firestore/test_firestore_session_service.py
+++ b/tests/unittests/integrations/firestore/test_firestore_session_service.py
@@ -399,6 +399,7 @@ async def test_list_sessions_with_user_id(mock_firestore_client):
       "appName": app_name,
       "userId": user_id,
       "state": {"session_key": "session_val"},
+      "updateTime": 1234567890.0,
   }
 
   app_state_coll = mock.MagicMock()
@@ -454,6 +455,7 @@ def collection_side_effect(name):
   assert session.state["session_key"] == "session_val"
   assert session.state["app:app_key"] == "app_val"
   assert session.state["user:user_key"] == "user_val"
+  assert session.last_update_time == 1234567890.0
 
 
 @pytest.mark.asyncio
@@ -467,6 +469,7 @@ async def test_list_sessions_without_user_id(mock_firestore_client):
       "appName": app_name,
       "userId": "user1",
       "state": {"session_key": "session_val"},
+      "updateTime": 1234567890.0,
   }
 
   mock_firestore_client.collection_group.return_value.where.return_value.get = (
@@ -508,6 +511,7 @@ def collection_side_effect(name):
   assert session.id == "session1"
   assert session.state["app:app_key"] == "app_val"
   assert session.state["user:user_key"] == "user_val"
+  assert session.last_update_time == 1234567890.0
 
   mock_firestore_client.collection_group.assert_called_once_with("sessions")
   mock_firestore_client.collection_group.return_value.where.assert_called_once_with(