diff --git a/api/services/tools/mcp_tools_manage_service.py b/api/services/tools/mcp_tools_manage_service.py
index 2b52615338e307..763c7b44158b0e 100644
--- a/api/services/tools/mcp_tools_manage_service.py
+++ b/api/services/tools/mcp_tools_manage_service.py
@@ -800,12 +800,20 @@ def _process_headers(self, headers: dict[str, str], mcp_provider: MCPToolProvide
     def _process_credentials(
         self, authentication: MCPAuthentication, mcp_provider: MCPToolProvider, tenant_id: str
     ) -> str:
-        """Process credentials update, handling masked values."""
+        """Process credentials update, handling masked values and keeping stored OAuth state when unchanged."""
         # Merge with existing credentials
         final_client_id, final_client_secret = self._merge_credentials_with_masked(
             authentication.client_id, authentication.client_secret, mcp_provider
         )
 
+        existing_client_info = mcp_provider.to_entity().retrieve_client_information()
+        if (
+            existing_client_info
+            and final_client_id == existing_client_info.client_id
+            and final_client_secret == existing_client_info.client_secret
+        ):
+            return mcp_provider.encrypted_credentials or EMPTY_CREDENTIALS_JSON
+
         # Build and encrypt
         return self._build_and_encrypt_credentials(final_client_id, final_client_secret, tenant_id)
 
@@ -851,20 +859,24 @@ def _merge_credentials_with_masked(
             Tuple of (final_client_id, final_client_secret)
         """
         mcp_provider_entity = mcp_provider.to_entity()
-        existing_decrypted = mcp_provider_entity.decrypt_credentials()
+        existing_client_info = mcp_provider_entity.retrieve_client_information()
         existing_masked = mcp_provider_entity.masked_credentials()
 
         # Check if client_id is masked and unchanged
         final_client_id = client_id
-        if existing_masked.get("client_id") and client_id == existing_masked["client_id"]:
+        if existing_client_info and existing_masked.get("client_id") and client_id == existing_masked["client_id"]:
             # Use existing decrypted value
-            final_client_id = existing_decrypted.get("client_id", client_id)
+            final_client_id = existing_client_info.client_id
 
         # Check if client_secret is masked and unchanged
         final_client_secret = client_secret
-        if existing_masked.get("client_secret") and client_secret == existing_masked["client_secret"]:
+        if (
+            existing_client_info
+            and existing_masked.get("client_secret")
+            and client_secret == existing_masked["client_secret"]
+        ):
             # Use existing decrypted value
-            final_client_secret = existing_decrypted.get("client_secret", client_secret)
+            final_client_secret = existing_client_info.client_secret
 
         return final_client_id, final_client_secret
 
diff --git a/api/tests/unit_tests/services/tools/test_mcp_tools_manage_service.py b/api/tests/unit_tests/services/tools/test_mcp_tools_manage_service.py
index 95ef5320ed023f..cec0a005717197 100644
--- a/api/tests/unit_tests/services/tools/test_mcp_tools_manage_service.py
+++ b/api/tests/unit_tests/services/tools/test_mcp_tools_manage_service.py
@@ -1,14 +1,17 @@
 """Exercise tenant-scoped MCP provider lookups against persisted rows.
 
 Primary keys and server identifiers are distinct, even when an identifier looks
-like a UUID or collides with another provider's primary key.
+like a UUID or collides with another provider's primary key. Unchanged masked
+OAuth client credentials resolve to the stored client information on update.
 """
 
+import json
 from typing import Literal
 
 import pytest
 from sqlalchemy.orm import Session
 
+from core.entities.mcp_provider import MCPAuthentication, MCPConfiguration
 from models.tools import MCPToolProvider
 from services.tools.mcp_tools_manage_service import MCPToolManageService
 
@@ -158,3 +161,61 @@ def test_server_identifier_can_be_reused_across_tenants(service: MCPToolManageSe
         service.get_provider_by_server_identifier(server_identifier=SERVER_IDENTIFIER, tenant_id=TENANT_ID).id
         == provider.id
     )
+
+
+def test_merge_credentials_with_masked_restores_nested_client_information(
+    service: MCPToolManageService, sqlite_session: Session
+) -> None:
+    provider = _provider()
+    provider.encrypted_credentials = json.dumps(
+        {
+            "client_information": {
+                "client_id": "ba0f3e1c-registered-client-c2",
+                "client_secret": "dynamic-client-secret",
+                "redirect_uris": ["https://example.com/callback"],
+            }
+        }
+    )
+    _persist(sqlite_session, provider)
+    masked = provider.to_entity().masked_credentials()
+
+    assert service._merge_credentials_with_masked(masked["client_id"], masked["client_secret"], provider) == (
+        "ba0f3e1c-registered-client-c2",
+        "dynamic-client-secret",
+    )
+
+
+def test_update_provider_keeps_oauth_state_when_masked_credentials_are_unchanged(
+    service: MCPToolManageService, sqlite_session: Session
+) -> None:
+    provider = _provider()
+    credentials = json.dumps(
+        {
+            "client_information": {
+                "client_id": "ba0f3e1c-registered-client-c2",
+                "client_secret": "dynamic-client-secret",
+                "redirect_uris": ["https://example.com/callback"],
+                "is_dynamic_registration": True,
+            },
+            "access_token": "access-token",
+            "refresh_token": "refresh-token",
+        }
+    )
+    provider.encrypted_credentials = credentials
+    _persist(sqlite_session, provider)
+    masked = provider.to_entity().masked_credentials()
+
+    service.update_provider(
+        tenant_id=TENANT_ID,
+        provider_id=PROVIDER_UUID,
+        name="Renamed MCP",
+        server_url=provider.server_url,
+        icon="icon",
+        icon_type="link",
+        icon_background="",
+        server_identifier=SERVER_IDENTIFIER,
+        configuration=MCPConfiguration(),
+        authentication=MCPAuthentication(client_id=masked["client_id"], client_secret=masked["client_secret"]),
+    )
+
+    assert provider.encrypted_credentials == credentials