diff --git a/tests/test_cli.py b/tests/test_cli.py
index f4d0c33..f65ccd1 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -4,7 +4,7 @@
 import pathlib
 import tempfile
 import uuid
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 from random import randint
 from unittest import TestCase
 
@@ -125,7 +125,7 @@ def setUp(self) -> None:
             "startUrl": "https://petshop.awsapps.com/start",
             "region": "ap-southeast-2",
             "accessToken": "longTextA.AverylOngText",
-            "expiresAt": f"{str((datetime.utcnow() + timedelta(hours=3)).isoformat())[:-7]}UTC",
+            "expiresAt": f"{str((datetime.now(timezone.utc) + timedelta(hours=3)).isoformat())[:-7]}UTC",
             "clientId": "longTextA",
             "clientSecret": "longTextA",  # pragma: allowlist secret
             "refreshToken": "longTextA"   # pragma: allowlist secret
@@ -144,7 +144,7 @@ def setUp(self) -> None:
                     'accessKeyId': 'does-not-matter',
                     'secretAccessKey': '',
                     'sessionToken': 'VeryLongBase664String==',
-                    'expiration': datetime.utcnow().timestamp()
+                    'expiration': datetime.now(timezone.utc).timestamp()
                 }
         }
 
@@ -450,7 +450,7 @@ def test_sso_cache_refresh_token_does_not_exist(self):
                 "startUrl": "https://petshop.awsapps.com/start",
                 "region": "ap-southeast-2",
                 "accessToken": "longTextA.AverylOngText",
-                "expiresAt": f"{str((datetime.utcnow() + timedelta(hours=3)).isoformat())[:-7]}UTC",
+                "expiresAt": f"{str((datetime.now(timezone.utc) + timedelta(hours=3)).isoformat())[:-7]}UTC",
                 "clientId": "longTextA",
                 "clientSecret": "longTextA",  # pragma: allowlist secret
                 # Simulate 'refreshToken' does not exist in sso cache json file.
diff --git a/yawsso/core.py b/yawsso/core.py
index d949cec..873a524 100644
--- a/yawsso/core.py
+++ b/yawsso/core.py
@@ -48,7 +48,7 @@ def update_aws_cli_v1_credentials(profile_name, profile, credentials):
 
     # set expiration
     ts_expires_millisecond = credentials["expiration"]
-    dt_utc = str(datetime.utcfromtimestamp(ts_expires_millisecond / 1000.0).isoformat() + '+0000')
+    dt_utc = str(datetime.fromtimestamp(ts_expires_millisecond / 1000.0, timezone.utc).isoformat() + '+0000')
     config.set(profile_name, "aws_session_expiration", dt_utc)
 
     # set region
@@ -72,6 +72,7 @@ def parse_assume_role_credentials_expiry(dt_str):
 def parse_credentials_file_session_expiry(dt_str):
     datetime_format_in_cred_file_aws_session_expiration = "%Y-%m-%dT%H:%M:%S+0000"  # 2020-06-14T17:13:26+0000
     expires_utc = datetime.strptime(dt_str, datetime_format_in_cred_file_aws_session_expiration)
+    expires_utc = expires_utc.replace(tzinfo=timezone.utc)
     return expires_utc
 
 
@@ -190,7 +191,7 @@ def fetch_credentials_with_assume_role(profile_name, profile):
                           f"to a maximum of one hour. Well, you can always `yawsso` again when session expired!")
         duration_seconds = Constant.ROLE_CHAINING_DURATION_SECONDS.value
 
-    utc_now_ts = int(datetime.utcnow().replace(tzinfo=timezone.utc).timestamp())
+    utc_now_ts = int(datetime.now(timezone.utc).replace(tzinfo=timezone.utc).timestamp())
     cmd_assume_role_cred = f"{aws_bin} sts assume-role " \
                            f"--output json " \
                            f"--profile {profile['source_profile']} " \
@@ -228,7 +229,7 @@ def eager_sync_source_profile(source_profile_name, source_profile):
     if config.has_section(source_profile_name):
         cred_profile = dict(config.items(source_profile_name))
         session_expires_utc = parse_credentials_file_session_expiry(cred_profile['aws_session_expiration'])
-        if datetime.utcnow() > session_expires_utc:
+        if datetime.now(timezone.utc) > session_expires_utc:
             logger.log(TRACE, f"Eagerly sync source_profile `{source_profile_name}`")
             credentials = fetch_credentials(source_profile_name, source_profile)
             update_aws_cli_v1_credentials(source_profile_name, source_profile, credentials)