diff --git a/csst_common/time.py b/csst_common/time.py
index 4585138d6fa0fa418f14ec3a2be8bdc43ef36457..a6bd1f0fdc867d3a8f5326dfc8de86947c126cb0 100644
--- a/csst_common/time.py
+++ b/csst_common/time.py
@@ -7,15 +7,21 @@ Created:        2023-03-09
 Modified-History:
     2023-03-09, Bo Zhang, created
     2023-03-09, Bo Zhang, add two time formats
+    2023-12-20, Bo Zhang, use astropy.time
 """
-import datetime
+from astropy import time
 
 
 def now():
-    """Return ISOT8601 format datetime, for time stamps in data products."""
-    return datetime.datetime.now().strftime("%Y-%m-%dT%H:%M:%S.%f")
+    """Return ISOT format datetime using `astropy`."""
+    return time.Time.now().isot
 
 
-def now_dfs():
-    """Return ISOT8601 format datetime, for DFS usage only."""
-    return datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
+# def now():
+#     """Return ISOT8601 format datetime, for time stamps in data products."""
+#     return datetime.datetime.now().strftime("%Y-%m-%dT%H:%M:%S.%f")
+
+
+# def now_dfs():
+#     """Return ISOT8601 format datetime, for DFS usage only."""
+#     return datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")