diff --git a/changelog/change_rails_root_pathname_methods_to_detect_offenses_on_dir_index.md b/changelog/change_rails_root_pathname_methods_to_detect_offenses_on_dir_index.md
new file mode 100644
index 0000000000..30a32029f1
--- /dev/null
+++ b/changelog/change_rails_root_pathname_methods_to_detect_offenses_on_dir_index.md
@@ -0,0 +1 @@
+* [#1003](https://github.com/rubocop/rubocop-rails/pull/1003): Change `Rails/RootPathnameMethods` to detect offenses on `Dir.[]`. ([@r7kamura][])
diff --git a/lib/rubocop/cop/rails/root_pathname_methods.rb b/lib/rubocop/cop/rails/root_pathname_methods.rb
index da308656a4..233b1744d0 100644
--- a/lib/rubocop/cop/rails/root_pathname_methods.rb
+++ b/lib/rubocop/cop/rails/root_pathname_methods.rb
@@ -38,7 +38,7 @@ class RootPathnameMethods < Base # rubocop:disable Metrics/ClassLength
 
         MSG = '`%<rails_root>s` is a `Pathname` so you can just append `#%<method>s`.'
 
-        DIR_GLOB_METHODS = %i[glob].to_set.freeze
+        DIR_GLOB_METHODS = %i[[] glob].to_set.freeze
 
         DIR_NON_GLOB_METHODS = %i[
           children
@@ -171,7 +171,7 @@ class RootPathnameMethods < Base # rubocop:disable Metrics/ClassLength
 
         def_node_matcher :dir_glob?, <<~PATTERN
           (send
-            (const {cbase nil?} :Dir) :glob ...)
+            (const {cbase nil?} :Dir) DIR_GLOB_METHODS ...)
         PATTERN
 
         def_node_matcher :rails_root_pathname?, <<~PATTERN
@@ -190,7 +190,7 @@ def on_send(node)
           evidence(node) do |method, path, args, rails_root|
             add_offense(node, message: format(MSG, method: method, rails_root: rails_root.source)) do |corrector|
               replacement = if dir_glob?(node)
-                              build_path_glob_replacement(path, method)
+                              build_path_glob_replacement(path)
                             else
                               build_path_replacement(path, method, args)
                             end
@@ -217,12 +217,12 @@ def pathname_method(node)
           end
         end
 
-        def build_path_glob_replacement(path, method)
+        def build_path_glob_replacement(path)
           receiver = range_between(path.source_range.begin_pos, path.children.first.loc.selector.end_pos).source
 
           argument = path.arguments.one? ? path.first_argument.source : join_arguments(path.arguments)
 
-          "#{receiver}.#{method}(#{argument})"
+          "#{receiver}.glob(#{argument})"
         end
 
         def build_path_replacement(path, method, args)
diff --git a/spec/rubocop/cop/rails/root_pathname_methods_spec.rb b/spec/rubocop/cop/rails/root_pathname_methods_spec.rb
index fdeeeba603..04b9508073 100644
--- a/spec/rubocop/cop/rails/root_pathname_methods_spec.rb
+++ b/spec/rubocop/cop/rails/root_pathname_methods_spec.rb
@@ -2,15 +2,13 @@
 
 RSpec.describe RuboCop::Cop::Rails::RootPathnameMethods, :config do
   {
-    Dir: described_class::DIR_METHODS,
+    Dir: described_class::DIR_NON_GLOB_METHODS,
     File: described_class::FILE_METHODS,
     FileTest: described_class::FILE_TEST_METHODS,
     FileUtils: described_class::FILE_UTILS_METHODS,
     IO: described_class::FILE_METHODS
   }.each do |receiver, methods|
     methods.each do |method|
-      next if method == :glob
-
       it "registers an offense when using `#{receiver}.#{method}(Rails.public_path)` (if arity exists)" do
         expect_offense(<<~RUBY, receiver: receiver, method: method)
           %{receiver}.%{method}(Rails.public_path)
@@ -143,6 +141,19 @@
     end
   end
 
+  context 'when using Dir.[] on Ruby 2.5 or higher', :ruby25 do
+    it 'registers offense when using `Dir[Rails.root.join(...)]`' do
+      expect_offense(<<~RUBY)
+        Dir[Rails.root.join('spec/support/**/*.rb')]
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Rails.root` is a `Pathname` so you can just append `#[]`.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        Rails.root.glob('spec/support/**/*.rb')
+      RUBY
+    end
+  end
+
   # This is handled by `Rails/RootJoinChain`
   it 'does not register an offense when using `File.read(Rails.root.join(...).join(...))`' do
     expect_no_offenses(<<~RUBY)