diff -r 2a18f6b85da2 Doc/library/unittest.mock.rst
--- a/Doc/library/unittest.mock.rst	Sun Apr 12 18:47:56 2015 -0400
+++ b/Doc/library/unittest.mock.rst	Mon Apr 13 22:32:05 2015 +0530
@@ -336,7 +336,7 @@
         .. versionadded:: 3.5
 
 
-    .. method:: reset_mock()
+    .. method:: reset_mock(return_value=False, side_effect=False)
 
         The reset_mock method resets all the call attributes on a mock object:
 
@@ -351,7 +351,9 @@
         This can be useful where you want to make a series of assertions that
         reuse the same object. Note that :meth:`reset_mock` *doesn't* clear the
         return value, :attr:`side_effect` or any child attributes you have
-        set using normal assignment. Child mocks and the return value mock
+        set using normal assignment by default. In case you want to reset
+        return_value or :attr:`side_effect`, then pass the corresponding
+        parameter as `True`. Child mocks and the return value mock
         (if any) are reset as well.
 
 
diff -r 2a18f6b85da2 Lib/unittest/mock.py
--- a/Lib/unittest/mock.py	Sun Apr 12 18:47:56 2015 -0400
+++ b/Lib/unittest/mock.py	Mon Apr 13 22:32:05 2015 +0530
@@ -522,7 +522,7 @@
     side_effect = property(__get_side_effect, __set_side_effect)
 
 
-    def reset_mock(self):
+    def reset_mock(self, return_value=False, side_effect=False):
         "Restore the mock object to its initial state."
         self.called = False
         self.call_args = None
@@ -531,6 +531,11 @@
         self.call_args_list = _CallList()
         self.method_calls = _CallList()
 
+        if return_value:
+            self._mock_return_value = DEFAULT
+        if side_effect:
+            self._mock_side_effect = None
+
         for child in self._mock_children.values():
             if isinstance(child, _SpecState):
                 continue
diff -r 2a18f6b85da2 Lib/unittest/test/testmock/testmock.py
--- a/Lib/unittest/test/testmock/testmock.py	Sun Apr 12 18:47:56 2015 -0400
+++ b/Lib/unittest/test/testmock/testmock.py	Mon Apr 13 22:32:05 2015 +0530
@@ -1223,6 +1223,14 @@
         self.assertEqual(m.method_calls[0], c)
         self.assertEqual(m.method_calls[1], i)
 
+    #Issue21271 allow resetting return_value and side_effect
+    def test_reset_return_side(self):
+        m = Mock(return_value=10, side_effect=[2,3])
+        m.reset_mock(return_value=True, side_effect=True)
+        self.assertIsInstance(m.return_value, Mock)
+        self.assertEqual(m.side_effect, None)
+
+
     def test_mock_add_spec(self):
         class _One(object):
             one = 1