diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 422da05ba5f..eb112de1451 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,4 +1,4 @@
-image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.4.5-golang-1.9-git-2.18-chrome-69.0-node-10.x-yarn-1.12-postgresql-9.6-graphicsmagick-1.3.29"
+image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.5.3-golang-1.9-git-2.18-chrome-69.0-node-10.x-yarn-1.12-postgresql-9.6-graphicsmagick-1.3.29"
 
 .dedicated-runner: &dedicated-runner
   retry: 1
@@ -6,7 +6,7 @@ image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.4.5-golang-1.9-git
     - gitlab-org
 
 .default-cache: &default-cache
-  key: "debian-stretch-ruby-2.4.5-node-10.x"
+  key: "debian-stretch-ruby-2.5.3-node-10.x"
   paths:
     - vendor/ruby
     - .yarn-cache/
@@ -121,7 +121,7 @@ stages:
   <<: *except-docs-and-qa
 
 .single-script-job: &single-script-job
-  image: ruby:2.4-alpine
+  image: ruby:2.5-alpine
   stage: test
   cache: {}
   dependencies: []
@@ -227,6 +227,8 @@ stages:
   script:
     - git fetch https://gitlab.com/gitlab-org/gitlab-ce.git v9.3.0
     - git checkout -f FETCH_HEAD
+    - sed -i "s/gem 'oj', '~> 2.17.4'//" Gemfile
+    - bundle update google-protobuf grpc
     - bundle install $BUNDLE_INSTALL_FLAGS
     - date
     - cp config/gitlab.yml.example config/gitlab.yml
@@ -316,7 +318,7 @@ review-docs-cleanup:
 # Trigger a docker image build in CNG (Cloud Native GitLab) repository
 #
 cloud-native-image:
-  image: ruby:2.4-alpine
+  image: ruby:2.5-alpine
   before_script: []
   dependencies: []
   stage: test
@@ -369,7 +371,7 @@ update-tests-metadata:
 
 flaky-examples-check:
   <<: *dedicated-runner
-  image: ruby:2.4-alpine
+  image: ruby:2.5-alpine
   services: []
   before_script: []
   variables:
@@ -589,7 +591,7 @@ static-analysis:
   script:
     - scripts/static-analysis
   cache:
-    key: "debian-stretch-ruby-2.4.5-node-10.x-and-rubocop"
+    key: "debian-stretch-ruby-2.5.3-node-10.x-and-rubocop"
     paths:
       - vendor/ruby
       - .yarn-cache/
@@ -696,7 +698,7 @@ gitlab:setup-mysql:
 # Frontend-related jobs
 gitlab:assets:compile:
   <<: *dedicated-no-docs-and-no-qa-pull-cache-job
-  image: dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.4.4-git-2.18-chrome-69.0-node-8.x-yarn-1.2-graphicsmagick-1.3.29-docker-18.06.1
+  image: dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.5.3-git-2.18-chrome-69.0-node-8.x-yarn-1.2-graphicsmagick-1.3.29-docker-18.06.1
   dependencies: []
   services:
     - docker:stable-dind
diff --git a/.ruby-version b/.ruby-version
index 59aa62c1fa4..aedc15bb0c6 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-2.4.5
+2.5.3
diff --git a/changelogs/unreleased/sh-bump-ruby-2-5-3.yml b/changelogs/unreleased/sh-bump-ruby-2-5-3.yml
new file mode 100644
index 00000000000..13cadc73e9c
--- /dev/null
+++ b/changelogs/unreleased/sh-bump-ruby-2-5-3.yml
@@ -0,0 +1,5 @@
+---
+title: Upgrade to Ruby 2.5.3
+merge_request: 2806
+author:
+type: performance
diff --git a/doc/install/installation.md b/doc/install/installation.md
index 316411d1047..cac97b63d92 100644
--- a/doc/install/installation.md
+++ b/doc/install/installation.md
@@ -132,9 +132,9 @@ Remove the old Ruby 1.8 if present:
 Download Ruby and compile it:
 
     mkdir /tmp/ruby && cd /tmp/ruby
-    curl --remote-name --progress https://cache.ruby-lang.org/pub/ruby/2.4/ruby-2.4.5.tar.gz
-    echo '4d650f302f1ec00256450b112bb023644b6ab6dd  ruby-2.4.5.tar.gz' | shasum -c - && tar xzf ruby-2.4.5.tar.gz
-    cd ruby-2.4.5
+    curl --remote-name --progress https://cache.ruby-lang.org/pub/ruby/2.5/ruby-2.5.3.tar.gz
+    echo 'f919a9fbcdb7abecd887157b49833663c5c15fda  ruby-2.5.3.tar.gz' | shasum -c - && tar xzf ruby-2.5.3.tar.gz
+    cd ruby-2.5.3
 
     ./configure --disable-install-rdoc
     make