diff --git a/ruby/1299-replace-elements-with-greatest-element-on-right-side.rb b/ruby/1299-replace-elements-with-greatest-element-on-right-side.rb
new file mode 100644
index 000000000..5756a5480
--- /dev/null
+++ b/ruby/1299-replace-elements-with-greatest-element-on-right-side.rb
@@ -0,0 +1,9 @@
+def replace_elements(arr)
+  right_max = -1
+  (arr.length - 1).downto(0) do |i|
+    cur_max = [right_max, arr[i]].max
+    arr[i] = right_max
+    right_max = cur_max
+  end
+  arr
+end