diff --git a/backend/open_webui/routers/auths.py b/backend/open_webui/routers/auths.py
index 16ae0422e8..a07d5ed678 100644
--- a/backend/open_webui/routers/auths.py
+++ b/backend/open_webui/routers/auths.py
@@ -75,6 +75,7 @@ from open_webui.utils.auth import (
     verify_password,
 )
 from open_webui.utils.groups import apply_default_group_assignment
+from open_webui.utils.json_codec import JSONCodec
 from open_webui.utils.misc import parse_duration, validate_email_format
 from open_webui.utils.rate_limit import RateLimiter
 from pydantic import BaseModel, StrictStr, field_validator
@@ -1463,6 +1464,9 @@ OAUTH_CONFIG_KEYS = {
 
 
 def _format_oauth_form_value(field: str, value):
+    if field == 'OAUTH_BLOCKED_GROUPS' and isinstance(value, list):
+        # Preserve commas in group names and regex patterns when the form is saved.
+        return JSONCodec.dumps(value)
     if field in OAUTH_COMMA_LIST_FIELDS and isinstance(value, list):
         return ','.join(str(item) for item in value)
     return value
diff --git a/backend/open_webui/utils/oauth.py b/backend/open_webui/utils/oauth.py
index 10dedb1e6c..ca8e3a1d75 100644
--- a/backend/open_webui/utils/oauth.py
+++ b/backend/open_webui/utils/oauth.py
@@ -351,6 +351,19 @@ def is_in_blocked_groups(group_name: str, groups: list) -> bool:
     return False
 
 
+def _parse_blocked_groups(value) -> list[str]:
+    """Accept JSON arrays, persisted lists, and comma-separated admin input."""
+    if isinstance(value, str):
+        try:
+            parsed = JSONCodec.loads(value)
+        except JSONCodec.JSONDecodeError:
+            parsed = None
+        value = parsed if isinstance(parsed, list) else [group.strip() for group in value.split(',')]
+    if not isinstance(value, list):
+        return []
+    return [group for group in value if isinstance(group, str) and group]
+
+
 def get_parsed_and_base_url(server_url) -> tuple[urllib.parse.ParseResult, str]:
     parsed = urllib.parse.urlparse(server_url)
     base_url = f'{parsed.scheme}://{parsed.netloc}'
@@ -1636,11 +1649,7 @@ class OAuthManager:
         log.debug('Running OAUTH Group management')
         oauth_claim = auth_config.OAUTH_GROUPS_CLAIM
 
-        try:
-            blocked_groups = JSONCodec.loads(auth_config.OAUTH_BLOCKED_GROUPS)
-        except Exception as e:
-            log.exception(f'Error loading OAUTH_BLOCKED_GROUPS: {e}')
-            blocked_groups = []
+        blocked_groups = _parse_blocked_groups(auth_config.OAUTH_BLOCKED_GROUPS)
 
         user_oauth_groups = []
         # Nested claim search for groups claim