diff --git a/tests/compute_engine/test__metadata.py b/tests/compute_engine/test__metadata.py
index 0898e1f..6a44585 100644
--- a/tests/compute_engine/test__metadata.py
+++ b/tests/compute_engine/test__metadata.py
@@ -16,7 +16,7 @@ import datetime
 import json
 import os
 
-import mock
+from unittest import mock
 import pytest
 from six.moves import http_client
 from six.moves import reload_module
diff --git a/tests/compute_engine/test_credentials.py b/tests/compute_engine/test_credentials.py
index ec9d13b..555306c 100644
--- a/tests/compute_engine/test_credentials.py
+++ b/tests/compute_engine/test_credentials.py
@@ -14,7 +14,7 @@
 
 import datetime
 
-import mock
+from unittest import mock
 import pytest
 
 from google.auth import _helpers
diff --git a/tests/conftest.py b/tests/conftest.py
index 2ccc132..de254f2 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -14,7 +14,7 @@
 
 import sys
 
-import mock
+from unittest import mock
 import pytest
 
 
diff --git a/tests/crypt/test__python_rsa.py b/tests/crypt/test__python_rsa.py
index 08b9503..e0be561 100644
--- a/tests/crypt/test__python_rsa.py
+++ b/tests/crypt/test__python_rsa.py
@@ -15,7 +15,7 @@
 import json
 import os
 
-import mock
+from unittest import mock
 from pyasn1_modules import pem
 import pytest
 import rsa
diff --git a/tests/oauth2/test__client.py b/tests/oauth2/test__client.py
index 052390a..beca8e8 100644
--- a/tests/oauth2/test__client.py
+++ b/tests/oauth2/test__client.py
@@ -16,7 +16,7 @@ import datetime
 import json
 import os
 
-import mock
+from unittest import mock
 import pytest
 import six
 from six.moves import http_client
diff --git a/tests/oauth2/test_credentials.py b/tests/oauth2/test_credentials.py
index af10f2f..5d9e239 100644
--- a/tests/oauth2/test_credentials.py
+++ b/tests/oauth2/test_credentials.py
@@ -18,7 +18,7 @@ import os
 import pickle
 import sys
 
-import mock
+from unittest import mock
 import pytest
 
 from google.auth import _helpers
diff --git a/tests/oauth2/test_id_token.py b/tests/oauth2/test_id_token.py
index 980a8e9..d837c0e 100644
--- a/tests/oauth2/test_id_token.py
+++ b/tests/oauth2/test_id_token.py
@@ -14,7 +14,7 @@
 
 import json
 
-import mock
+from unittest import mock
 import pytest
 
 from google.auth import exceptions
diff --git a/tests/oauth2/test_service_account.py b/tests/oauth2/test_service_account.py
index 0f9d460..ba0f0fe 100644
--- a/tests/oauth2/test_service_account.py
+++ b/tests/oauth2/test_service_account.py
@@ -16,7 +16,7 @@ import datetime
 import json
 import os
 
-import mock
+from unittest import mock
 
 from google.auth import _helpers
 from google.auth import crypt
diff --git a/tests/test__cloud_sdk.py b/tests/test__cloud_sdk.py
index c5c5c27..96b6327 100644
--- a/tests/test__cloud_sdk.py
+++ b/tests/test__cloud_sdk.py
@@ -17,7 +17,7 @@ import json
 import os
 import subprocess
 
-import mock
+from unittest import mock
 import pytest
 
 from google.auth import _cloud_sdk
diff --git a/tests/test__default.py b/tests/test__default.py
index 2c86f3f..ba88982 100644
--- a/tests/test__default.py
+++ b/tests/test__default.py
@@ -15,7 +15,7 @@
 import json
 import os
 
-import mock
+from unittest import mock
 import pytest
 
 from google.auth import _default
diff --git a/tests/test__oauth2client.py b/tests/test__oauth2client.py
index 520f943..b1d2ece 100644
--- a/tests/test__oauth2client.py
+++ b/tests/test__oauth2client.py
@@ -16,7 +16,7 @@ import datetime
 import os
 import sys
 
-import mock
+from unittest import mock
 import oauth2client.client
 import oauth2client.contrib.gce
 import oauth2client.service_account
diff --git a/tests/test_app_engine.py b/tests/test_app_engine.py
index 9559a2c..29ca4f0 100644
--- a/tests/test_app_engine.py
+++ b/tests/test_app_engine.py
@@ -14,7 +14,7 @@
 
 import datetime
 
-import mock
+from unittest import mock
 import pytest
 
 from google.auth import app_engine
diff --git a/tests/test_iam.py b/tests/test_iam.py
index 52ab9bd..f852cca 100644
--- a/tests/test_iam.py
+++ b/tests/test_iam.py
@@ -16,7 +16,7 @@ import base64
 import datetime
 import json
 
-import mock
+from unittest import mock
 import pytest
 from six.moves import http_client
 
diff --git a/tests/test_impersonated_credentials.py b/tests/test_impersonated_credentials.py
index 1cfcc7c..4449762 100644
--- a/tests/test_impersonated_credentials.py
+++ b/tests/test_impersonated_credentials.py
@@ -16,7 +16,7 @@ import datetime
 import json
 import os
 
-import mock
+from unittest import mock
 import pytest
 from six.moves import http_client
 
diff --git a/tests/test_jwt.py b/tests/test_jwt.py
index b0c6e48..ed6ce28 100644
--- a/tests/test_jwt.py
+++ b/tests/test_jwt.py
@@ -17,7 +17,7 @@ import datetime
 import json
 import os
 
-import mock
+from unittest import mock
 import pytest
 
 from google.auth import _helpers
diff --git a/tests/transport/test_grpc.py b/tests/transport/test_grpc.py
index ca12385..9fdb92d 100644
--- a/tests/transport/test_grpc.py
+++ b/tests/transport/test_grpc.py
@@ -15,7 +15,7 @@
 import datetime
 import time
 
-import mock
+from unittest import mock
 import pytest
 
 from google.auth import _helpers
diff --git a/tests/transport/test_requests.py b/tests/transport/test_requests.py
index f0321c8..f393950 100644
--- a/tests/transport/test_requests.py
+++ b/tests/transport/test_requests.py
@@ -16,7 +16,7 @@ import datetime
 import functools
 
 import freezegun
-import mock
+from unittest import mock
 import pytest
 import requests
 import requests.adapters
diff --git a/tests/transport/test_urllib3.py b/tests/transport/test_urllib3.py
index 1d7ce5a..627b33c 100644
--- a/tests/transport/test_urllib3.py
+++ b/tests/transport/test_urllib3.py
@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import mock
+from unittest import mock
 from six.moves import http_client
 import urllib3