diff --git a/django/core/serializers/json.py b/django/core/serializers/json.py
index b955939e0d04..4b4f7f30c032 100644
--- a/django/core/serializers/json.py
+++ b/django/core/serializers/json.py
@@ -90,9 +90,10 @@ class DjangoJSONEncoder(json.JSONEncoder):
     def default(self, o):
         # See "Date Time String Format" in the ECMA-262 specification.
         if isinstance(o, datetime.datetime):
-            r = o.isoformat()
-            if o.microsecond:
-                r = r[:23] + r[26:]
+            r = o.isoformat(
+                sep="T",
+                timespec="milliseconds" if o.microsecond // 1000 else "seconds",
+            )
             if r.endswith("+00:00"):
                 r = r.removesuffix("+00:00") + "Z"
             return r
@@ -101,9 +102,9 @@ def default(self, o):
         elif isinstance(o, datetime.time):
             if is_aware(o):
                 raise ValueError("JSON can't represent timezone-aware times.")
-            r = o.isoformat()
-            if o.microsecond:
-                r = r[:12]
+            r = o.isoformat(
+                timespec="milliseconds" if o.microsecond // 1000 else "seconds"
+            )
             return r
         elif isinstance(o, datetime.timedelta):
             return duration_iso_string(o)
diff --git a/docs/releases/6.2.txt b/docs/releases/6.2.txt
index 1193f7a84d89..3bafa4f583e0 100644
--- a/docs/releases/6.2.txt
+++ b/docs/releases/6.2.txt
@@ -256,6 +256,12 @@ Miscellaneous
   pollution vulnerability in the ``Array`` prototype was fixed in
   `ES5 <https://262.ecma-international.org/5.1/#sec-11.1.4>`_.
 
+* :class:`~django.core.serializers.json.DjangoJSONEncoder` now omits the
+  millisecond component of serialized ``datetime.datetime`` and
+  ``datetime.time`` objects if they have zero milliseconds. For example,
+  ``datetime.datetime(2000, 1, 1, 0, 0, 0, 1)`` now serializes to
+  ``"2000-01-01T00:00:00"`` rather than ``"2000-01-01T00:00:00.000"``.
+
 .. _deprecated-features-6.2:
 
 Features deprecated in 6.2
diff --git a/tests/serializers/test_json.py b/tests/serializers/test_json.py
index 2c8ad5708e64..6f527fa4a064 100644
--- a/tests/serializers/test_json.py
+++ b/tests/serializers/test_json.py
@@ -329,3 +329,28 @@ def test_timedelta(self):
             json.dumps({"duration": duration}, cls=DjangoJSONEncoder),
             '{"duration": "P0DT00H00M00S"}',
         )
+
+    def test_datetime_and_time_microseconds(self):
+        tests = [
+            (datetime.datetime(2000, 1, 1, 0, 0, 0, 0), '"2000-01-01T00:00:00"'),
+            (datetime.datetime(2000, 1, 1, 0, 0, 0, 1), '"2000-01-01T00:00:00"'),
+            (
+                datetime.datetime(2000, 1, 1, 0, 0, 0, 1000),
+                '"2000-01-01T00:00:00.001"',
+            ),
+            (
+                datetime.datetime(2000, 1, 1, 0, 0, 0, 1001),
+                '"2000-01-01T00:00:00.001"',
+            ),
+            (
+                datetime.datetime(2000, 1, 1, 0, 0, 0, 123000),
+                '"2000-01-01T00:00:00.123"',
+            ),
+            (datetime.time(0, 0, 0, 0), '"00:00:00"'),
+            (datetime.time(0, 0, 0, 1), '"00:00:00"'),
+            (datetime.time(0, 0, 0, 1000), '"00:00:00.001"'),
+            (datetime.time(0, 0, 0, 123000), '"00:00:00.123"'),
+        ]
+        for value, expected in tests:
+            with self.subTest(value=value):
+                self.assertEqual(json.dumps(value, cls=DjangoJSONEncoder), expected)