diff --git a/lower-constraints.txt b/lower-constraints.txt
index 897fce1..f708475 100644
--- a/lower-constraints.txt
+++ b/lower-constraints.txt
@@ -30,7 +30,6 @@ keystoneauth1==3.4.0
 linecache2==1.0.0
 MarkupSafe==1.0
 mccabe==0.2.1
-mock==2.0.0
 monotonic==0.6
 mox3==0.20.0
 msgpack-python==0.4.0
diff --git a/monascaclient/tests/test_client.py b/monascaclient/tests/test_client.py
index ebc1021..3d709ed 100644
--- a/monascaclient/tests/test_client.py
+++ b/monascaclient/tests/test_client.py
@@ -14,9 +14,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from unittest import mock
 import warnings
 
-import mock
 from oslotest import base
 
 from monascaclient import client
diff --git a/monascaclient/tests/test_shell.py b/monascaclient/tests/test_shell.py
index bed27f1..5461670 100644
--- a/monascaclient/tests/test_shell.py
+++ b/monascaclient/tests/test_shell.py
@@ -14,7 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import mock
+from unittest import mock
 
 from oslotest import base
 
diff --git a/monascaclient/tests/v2_0/shell/test_alarm_definitions.py b/monascaclient/tests/v2_0/shell/test_alarm_definitions.py
index a844b11..61c8f7d 100644
--- a/monascaclient/tests/v2_0/shell/test_alarm_definitions.py
+++ b/monascaclient/tests/v2_0/shell/test_alarm_definitions.py
@@ -12,7 +12,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-import mock
+from unittest import mock
 
 from oslotest import base
 
diff --git a/monascaclient/tests/v2_0/shell/test_metrics.py b/monascaclient/tests/v2_0/shell/test_metrics.py
index fd46530..fde6663 100644
--- a/monascaclient/tests/v2_0/shell/test_metrics.py
+++ b/monascaclient/tests/v2_0/shell/test_metrics.py
@@ -12,7 +12,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-import mock
+from unittest import mock
 
 from oslotest import base
 
diff --git a/monascaclient/tests/v2_0/shell/test_notification_types.py b/monascaclient/tests/v2_0/shell/test_notification_types.py
index 80919dc..74291b5 100644
--- a/monascaclient/tests/v2_0/shell/test_notification_types.py
+++ b/monascaclient/tests/v2_0/shell/test_notification_types.py
@@ -12,7 +12,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-import mock
+from unittest import mock
 
 from oslotest import base
 
diff --git a/monascaclient/tests/v2_0/shell/test_notifications.py b/monascaclient/tests/v2_0/shell/test_notifications.py
index 1c7015c..878e877 100644
--- a/monascaclient/tests/v2_0/shell/test_notifications.py
+++ b/monascaclient/tests/v2_0/shell/test_notifications.py
@@ -12,7 +12,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-import mock
+from unittest import mock
 
 from oslotest import base