diff --git a/.github/workflows/run-tests.yml b/.github/workflows/run-tests.yml
index 4bb0144..71f3993 100644
--- a/.github/workflows/run-tests.yml
+++ b/.github/workflows/run-tests.yml
@@ -16,7 +16,7 @@ jobs:
         fess-version:
           - fess_version: "14.19.2"
             opensearch_version: "2.19.1"
-          - fess_version: "15.3.2"
+          - fess_version: "15.4.0"
             opensearch_version: "3.3.2"
 
     steps:
diff --git a/README.md b/README.md
index beba259..213f1b6 100644
--- a/README.md
+++ b/README.md
@@ -25,7 +25,7 @@ The easiest way to get started is using the pre-built Docker image:
 docker run --rm \
   -e FESS_ENDPOINT=https://your-fess-server \
   -e FESS_ACCESS_TOKEN=your_access_token_here \
-  -e FESS_VERSION=15.3.2 \
+  -e FESS_VERSION=15.4.0 \
   ghcr.io/codelibs/fessctl:0.1.0 --help
 ```
 
@@ -35,13 +35,13 @@ Run actual commands:
 docker run --rm \
   -e FESS_ENDPOINT=https://your-fess-server \
   -e FESS_ACCESS_TOKEN=your_access_token_here \
-  -e FESS_VERSION=15.3.2 \
+  -e FESS_VERSION=15.4.0 \
   ghcr.io/codelibs/fessctl:0.1.0 ping
 
 docker run --rm \
   -e FESS_ENDPOINT=https://your-fess-server \
   -e FESS_ACCESS_TOKEN=your_access_token_here \
-  -e FESS_VERSION=15.3.2 \
+  -e FESS_VERSION=15.4.0 \
   ghcr.io/codelibs/fessctl:0.1.0 user list
 ```
 
@@ -61,7 +61,7 @@ Then run with your custom image:
 docker run --rm \
   -e FESS_ENDPOINT=https://your-fess-server \
   -e FESS_ACCESS_TOKEN=your_access_token_here \
-  -e FESS_VERSION=15.3.2 \
+  -e FESS_VERSION=15.4.0 \
   fessctl:latest --help
 ```
 
@@ -86,7 +86,7 @@ uv pip install -e src
 ```bash
 export FESS_ACCESS_TOKEN=your_access_token_here
 export FESS_ENDPOINT=https://your-fess-server
-export FESS_VERSION=15.3.2
+export FESS_VERSION=15.4.0
 
 fessctl --help
 fessctl ping
@@ -100,7 +100,7 @@ All three methods require the following environment variables:
 
 - `FESS_ENDPOINT`: The URL of your Fess server's API endpoint (default: `http://localhost:8080`)
 - `FESS_ACCESS_TOKEN`: Bearer token for API authentication (required)
-- `FESS_VERSION`: Target Fess version for API compatibility (default: `15.3.2`)
+- `FESS_VERSION`: Target Fess version for API compatibility (default: `15.4.0`)
 
 ## License
 
diff --git a/src/fessctl/config/settings.py b/src/fessctl/config/settings.py
index 4b706d7..8b7fefe 100644
--- a/src/fessctl/config/settings.py
+++ b/src/fessctl/config/settings.py
@@ -9,4 +9,4 @@ class Settings:
     access_token: str | None = field(
         default_factory=lambda: os.getenv("FESS_ACCESS_TOKEN", None))
     fess_version: str = field(
-        default_factory=lambda: os.getenv("FESS_VERSION", "15.3.2"))
+        default_factory=lambda: os.getenv("FESS_VERSION", "15.4.0"))
diff --git a/tests/compose-fess15.yaml b/tests/compose-fess15.yaml
index d8a6af2..5a2b6e2 100644
--- a/tests/compose-fess15.yaml
+++ b/tests/compose-fess15.yaml
@@ -1,11 +1,11 @@
 services:
   fessctl_fess01:
-    image: ghcr.io/codelibs/fess:${FESS_VERSION:-15.3.2}
+    image: ghcr.io/codelibs/fess:${FESS_VERSION:-15.4.0}
     container_name: fessctl_fess01
     environment:
       - "SEARCH_ENGINE_HTTP_URL=http://fessctl_search01:9200"
       - "FESS_DICTIONARY_PATH=${FESS_DICTIONARY_PATH:-/usr/share/opensearch/config/dictionary/}"
-#      - "FESS_PLUGINS=fess-ds-csv:${FESS_VERSION:-15.3.2}"
+#      - "FESS_PLUGINS=fess-ds-csv:${FESS_VERSION:-15.4.0}"
     volumes:
 #      - fessctl_fess01_plugin:/usr/share/fess/app/WEB-INF/plugin
       - ./resources/access_token.bulk:/usr/share/fess/app/WEB-INF/classes/fess_indices/fess_config.access_token/access_token.bulk