diff --git a/Dockerfile b/Dockerfile
index 3ca81d2..bef1eff 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,5 +1,5 @@
 # pull official base image
-FROM python:3.10-slim-buster
+FROM python:3.10-slim-bullseye
 
 # set work directory
 WORKDIR /usr/src/app
diff --git a/README.md b/README.md
index d668b56..93192b9 100644
--- a/README.md
+++ b/README.md
@@ -12,6 +12,10 @@ python3 manage.py runserver 0.0.0.0:8000
 gunicorn auth_prj.wsgi:application --bind 0.0.0.0:8000 --workers 3
 ```
 
+## 2025-09-28 RS256변경 적용 ( v0.0.13 )
+* Docker Build base image 변경. 
+    * python:3.10-slim-buster > python:3.10-slim-bullseye
+    
 ## 2025-09-28 RS256변경 적용 ( v0.0.12 )
 * 비대칭키 방식 → Private Key로 서명, Public Key로 검증.
 * 토큰 발급 서버는 Private Key만 보관.