diff --git a/README.md b/README.md
index 1ae6e33a..9acf4b2c 100644
--- a/README.md
+++ b/README.md
@@ -591,3 +591,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 523. Continuous Subarray Sum                                    | [Link](https://leetcode.com/problems/continuous-subarray-sum/)                                    | [Link](./lib/medium/523_continuous_subarray_sum.rb)                                    | [Link](./test/medium/test_523_continuous_subarray_sum.rb)                                    |
 | 524. Longest Word in Dictionary through Deleting                | [Link](https://leetcode.com/problems/longest-word-in-dictionary-through-deleting/)                | [Link](./lib/medium/524_longest_word_in_dictionary_through_deleting.rb)                | [Link](./test/medium/test_524_longest_word_in_dictionary_through_deleting.rb)                |
 | 535. Encode and Decode TinyURL                                  | [Link](https://leetcode.com/problems/encode-and-decode-tinyurl/)                                  | [Link](./lib/medium/535_encode_and_decode_tinyurl.rb)                                  | [Link](./test/medium/test_535_encode_and_decode_tinyurl.rb)                                  |
+| 538. Convert BST to Greater Tree                                | [Link](https://leetcode.com/problems/convert-bst-to-greater-tree/)                                | [Link](./lib/medium/538_convert_bst_to_greater_tree.rb)                                | [Link](./test/medium/test_538_convert_bst_to_greater_tree.rb)                                |
diff --git a/leetcode-ruby.gemspec b/leetcode-ruby.gemspec
index 408dd964..9902796a 100644
--- a/leetcode-ruby.gemspec
+++ b/leetcode-ruby.gemspec
@@ -5,7 +5,7 @@ require 'English'
 ::Gem::Specification.new do |s|
   s.required_ruby_version = '>= 3.0'
   s.name = 'leetcode-ruby'
-  s.version = '7.2.5'
+  s.version = '7.2.6'
   s.license = 'MIT'
   s.files = ::Dir['lib/**/*.rb'] + %w[README.md]
   s.executable = 'leetcode-ruby'
diff --git a/lib/medium/538_convert_bst_to_greater_tree.rb b/lib/medium/538_convert_bst_to_greater_tree.rb
new file mode 100644
index 00000000..24c75753
--- /dev/null
+++ b/lib/medium/538_convert_bst_to_greater_tree.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+$sum = 0
+
+# https://leetcode.com/problems/convert-bst-to-greater-tree/
+# @param {TreeNode} root
+# @return {TreeNode}
+def convert_bst(root)
+  $sum = 0
+
+  convert_bst_with_sum(root)
+end
+
+private
+
+# @param {TreeNode} node
+# @return {TreeNode}
+def convert_bst_with_sum(node)
+  return unless node
+
+  convert_bst_with_sum(node.right)
+  $sum += node.val
+  node.val = $sum
+  convert_bst_with_sum(node.left)
+
+  node
+end
diff --git a/test/medium/test_538_convert_bst_to_greater_tree.rb b/test/medium/test_538_convert_bst_to_greater_tree.rb
new file mode 100644
index 00000000..20a89095
--- /dev/null
+++ b/test/medium/test_538_convert_bst_to_greater_tree.rb
@@ -0,0 +1,78 @@
+# frozen_string_literal: true
+
+require_relative '../test_helper'
+require_relative '../../lib/common/binary_tree'
+require_relative '../../lib/medium/538_convert_bst_to_greater_tree'
+require 'minitest/autorun'
+
+class ConvertBstToGreaterTreeTest < ::Minitest::Test
+  def test_default_one
+    assert(
+      ::TreeNode.are_equals(
+        ::TreeNode.new(
+          30,
+          ::TreeNode.new(
+            36,
+            ::TreeNode.new(36),
+            ::TreeNode.new(
+              35,
+              nil,
+              ::TreeNode.new(33)
+            )
+          ),
+          ::TreeNode.new(
+            21,
+            ::TreeNode.new(26),
+            ::TreeNode.new(
+              15,
+              nil,
+              ::TreeNode.new(8)
+            )
+          )
+        ),
+        convert_bst(
+          ::TreeNode.new(
+            4,
+            ::TreeNode.new(
+              1,
+              ::TreeNode.new(0),
+              ::TreeNode.new(
+                2,
+                nil,
+                ::TreeNode.new(3)
+              )
+            ),
+            ::TreeNode.new(
+              6,
+              ::TreeNode.new(5),
+              ::TreeNode.new(
+                7,
+                nil,
+                ::TreeNode.new(8)
+              )
+            )
+          )
+        )
+      )
+    )
+  end
+
+  def test_default_two
+    assert(
+      ::TreeNode.are_equals(
+        ::TreeNode.new(
+          1,
+          nil,
+          ::TreeNode.new(1)
+        ),
+        convert_bst(
+          ::TreeNode.new(
+            0,
+            nil,
+            ::TreeNode.new(1)
+          )
+        )
+      )
+    )
+  end
+end