diff --git a/httpx/_transports/mock.py b/httpx/_transports/mock.py
index 8c418f59e0..dd382a9772 100644
--- a/httpx/_transports/mock.py
+++ b/httpx/_transports/mock.py
@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import datetime
 import typing
 
 from .._models import Request, Response
@@ -24,6 +25,7 @@ def handle_request(
         response = self.handler(request)
         if not isinstance(response, Response):  # pragma: no cover
             raise TypeError("Cannot use an async handler in a sync Client")
+        response.elapsed = datetime.timedelta(seconds=0)
         return response
 
     async def handle_async_request(
@@ -40,4 +42,5 @@ async def handle_async_request(
         if not isinstance(response, Response):
             response = await response
 
+        response.elapsed = datetime.timedelta(seconds=0)
         return response
diff --git a/tests/test_transports.py b/tests/test_transports.py
new file mode 100644
index 0000000000..56a3c574ec
--- /dev/null
+++ b/tests/test_transports.py
@@ -0,0 +1,24 @@
+import datetime
+import pytest
+import httpx
+
+
+def test_mock_transport_sets_elapsed():
+    """Test that MockTransport sets the elapsed property on responses."""
+    
+    # 1. Create a simple handler that returns a response
+    def handler(request: httpx.Request) -> httpx.Response:
+        return httpx.Response(200, content=b"Hello")
+    
+    # 2. Create a MockTransport with that handler
+    transport = httpx.MockTransport(handler)
+    
+    # 3. Create a client with the transport
+    client = httpx.Client(transport=transport)
+    
+    # 4. Make a request
+    response = client.get("http://example.com/")
+    
+    # 5. Assert that elapsed is set and is a timedelta
+    assert hasattr(response, "_elapsed")
+    assert isinstance(response.elapsed, datetime.timedelta)