diff --git a/docs/topics/extensions.rst b/docs/topics/extensions.rst
index 78b38cc3f..6d61cc342 100644
--- a/docs/topics/extensions.rst
+++ b/docs/topics/extensions.rst
@@ -374,8 +374,8 @@ This extension periodically logs rich stat data as a JSON object::
             "elapsed": 360.008903,
             "log_interval": 60.0,
             "log_interval_real": 60.006694,
-            "start_time": "2023-08-03 23:24:57",
-            "utcnow": "2023-08-03 23:30:57"
+            "start_time": "2023-08-03T23:24:57.148903+00:00",
+            "utcnow": "2023-08-03T23:30:57.157806+00:00"
         }
     }
 
diff --git a/scrapy/utils/serialize.py b/scrapy/utils/serialize.py
index 5d06bbe30..803b63bef 100644
--- a/scrapy/utils/serialize.py
+++ b/scrapy/utils/serialize.py
@@ -10,18 +10,11 @@ from scrapy.http import Request, Response
 
 
 class ScrapyJSONEncoder(json.JSONEncoder):
-    DATE_FORMAT = "%Y-%m-%d"
-    TIME_FORMAT = "%H:%M:%S"
-
     def default(self, o: Any) -> Any:
         if isinstance(o, set):
             return list(o)
-        if isinstance(o, datetime.datetime):
-            return o.strftime(f"{self.DATE_FORMAT} {self.TIME_FORMAT}")
-        if isinstance(o, datetime.date):
-            return o.strftime(self.DATE_FORMAT)
-        if isinstance(o, datetime.time):
-            return o.strftime(self.TIME_FORMAT)
+        if isinstance(o, (datetime.datetime, datetime.date, datetime.time)):
+            return o.isoformat()
         if isinstance(o, decimal.Decimal):
             return str(o)
         if isinstance(o, defer.Deferred):
diff --git a/tests/test_exporters.py b/tests/test_exporters.py
index 956697a04..4359f4ff4 100644
--- a/tests/test_exporters.py
+++ b/tests/test_exporters.py
@@ -578,7 +578,7 @@ class TestJsonLinesItemExporter(TestBaseItemExporter):
         self.ie.finish_exporting()
         del self.ie  # See the first “del self.ie” in this file for context.
         exported = json.loads(to_unicode(self.output.getvalue()))
-        item["time"] = str(item["time"])
+        item["time"] = item["time"].isoformat()
         assert exported == item
 
 
@@ -661,7 +661,7 @@ class TestJsonItemExporter(TestJsonLinesItemExporter):
         self.ie.finish_exporting()
         del self.ie  # See the first “del self.ie” in this file for context.
         exported = json.loads(to_unicode(self.output.getvalue()))
-        item["time"] = str(item["time"])
+        item["time"] = item["time"].isoformat()
         assert exported == [item]
 
 
diff --git a/tests/test_utils_serialize.py b/tests/test_utils_serialize.py
index 2702c2cce..6becad13e 100644
--- a/tests/test_utils_serialize.py
+++ b/tests/test_utils_serialize.py
@@ -20,11 +20,17 @@ class TestJsonEncoder:
 
     def test_encode_decode(self, encoder: ScrapyJSONEncoder) -> None:
         dt = datetime.datetime(2010, 1, 2, 10, 11, 12)
-        dts = "2010-01-02 10:11:12"
+        dts = "2010-01-02T10:11:12"
+        dt_aware = datetime.datetime(
+            2010, 1, 2, 10, 11, 12, 133700, tzinfo=datetime.timezone.utc
+        )
+        dt_awares = "2010-01-02T10:11:12.133700+00:00"
         d = datetime.date(2010, 1, 2)
         ds = "2010-01-02"
         t = datetime.time(10, 11, 12)
         ts = "10:11:12"
+        t_us = datetime.time(10, 11, 12, 133700)
+        t_uss = "10:11:12.133700"
         dec = Decimal("1000.12")
         decs = "1000.12"
         s = {"foo"}
@@ -36,7 +42,9 @@ class TestJsonEncoder:
             ("foo", "foo"),
             (d, ds),
             (t, ts),
+            (t_us, t_uss),
             (dt, dts),
+            (dt_aware, dt_awares),
             (dec, decs),
             (["foo", d], ["foo", ds]),
             (s, ss),