diff --git a/app/controllers/admin/groups_controller.rb b/app/controllers/admin/groups_controller.rb
index f28bbdeff5a..fc8d4d02ddf 100644
--- a/app/controllers/admin/groups_controller.rb
+++ b/app/controllers/admin/groups_controller.rb
@@ -43,9 +43,13 @@ class Admin::GroupsController < Admin::ApplicationController
   end
 
   def members_update
-    @group.add_users(params[:user_ids].split(','), params[:access_level], current_user: current_user)
+    status = Members::CreateService.new(@group, current_user, params).execute
 
-    redirect_to [:admin, @group], notice: 'Users were successfully added.'
+    if status
+      redirect_to [:admin, @group], notice: 'Users were successfully added.'
+    else
+      redirect_to [:admin, @group], alert: 'No users specified.'
+    end
   end
 
   def destroy
diff --git a/changelogs/unreleased/dz-refactor-admin-group-members.yml b/changelogs/unreleased/dz-refactor-admin-group-members.yml
new file mode 100644
index 00000000000..993a6cac0df
--- /dev/null
+++ b/changelogs/unreleased/dz-refactor-admin-group-members.yml
@@ -0,0 +1,4 @@
+---
+title: Refactor Admin::GroupsController#members_update method and add some specs
+merge_request: 10735
+author:
diff --git a/spec/controllers/admin/groups_controller_spec.rb b/spec/controllers/admin/groups_controller_spec.rb
index 84db26a958a..c29b2fe8946 100644
--- a/spec/controllers/admin/groups_controller_spec.rb
+++ b/spec/controllers/admin/groups_controller_spec.rb
@@ -22,4 +22,28 @@ describe Admin::GroupsController do
       expect(response).to redirect_to(admin_groups_path)
     end
   end
+
+  describe 'PUT #members_update' do
+    let(:group_user) { create(:user) }
+
+    it 'adds user to members' do
+      put :members_update, id: group,
+                           user_ids: group_user.id,
+                           access_level: Gitlab::Access::GUEST
+
+      expect(response).to set_flash.to 'Users were successfully added.'
+      expect(response).to redirect_to(admin_group_path(group))
+      expect(group.users).to include group_user
+    end
+
+    it 'adds no user to members' do
+      put :members_update, id: group,
+                           user_ids: '',
+                           access_level: Gitlab::Access::GUEST
+
+      expect(response).to set_flash.to 'No users specified.'
+      expect(response).to redirect_to(admin_group_path(group))
+      expect(group.users).not_to include group_user
+    end
+  end
 end