diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index e3a8e85567..b24d6b412f 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -1544,12 +1544,6 @@ class DecimalField(Field):
                 params={'value': value},
             )
 
-    def _format(self, value):
-        if isinstance(value, str):
-            return value
-        else:
-            return self.format_number(value)
-
     def format_number(self, value):
         """
         Format a number into a string with the requisite number of digits and
diff --git a/tests/model_fields/test_decimalfield.py b/tests/model_fields/test_decimalfield.py
index 5163d8188b..17bbae7ffa 100644
--- a/tests/model_fields/test_decimalfield.py
+++ b/tests/model_fields/test_decimalfield.py
@@ -28,12 +28,6 @@ class DecimalFieldTests(TestCase):
         f = models.DecimalField(default=Decimal('0.00'))
         self.assertEqual(f.get_default(), Decimal('0.00'))
 
-    def test_format(self):
-        f = models.DecimalField(max_digits=5, decimal_places=1)
-        self.assertEqual(f._format(f.to_python(2)), '2.0')
-        self.assertEqual(f._format(f.to_python('2.6')), '2.6')
-        self.assertIsNone(f._format(None))
-
     def test_get_prep_value(self):
         f = models.DecimalField(max_digits=5, decimal_places=1)
         self.assertIsNone(f.get_prep_value(None))