diff --git a/tests/test_memory_owner_isolation.py b/tests/test_memory_owner_isolation.py
new file mode 100644
index 000000000..ff32b9cd1
--- /dev/null
+++ b/tests/test_memory_owner_isolation.py
@@ -0,0 +1,28 @@
+from unittest.mock import MagicMock
+
+import routes.memory_routes as memory_routes
+from src.memory import MemoryManager
+
+
+def test_memory_search_returns_only_callers_memories(monkeypatch, tmp_path):
+    manager = MemoryManager(str(tmp_path))
+    alice_memory = manager.add_entry("Project codename is Odyssey", owner="alice")
+    bob_memory = manager.add_entry("Project codename is Odyssey", owner="bob")
+    manager.save([alice_memory, bob_memory])
+
+    monkeypatch.setattr(memory_routes, "get_current_user", lambda request: "bob")
+    router = memory_routes.setup_memory_routes(manager, MagicMock())
+    search = next(
+        route.endpoint
+        for route in router.routes
+        if route.path == "/api/memory/search" and "POST" in route.methods
+    )
+
+    result = search(
+        request=None,
+        query="Project codename is Odyssey",
+        session_id=None,
+        category=None,
+    )
+
+    assert [memory["id"] for memory in result["memories"]] == [bob_memory["id"]]