Moonstone (foaled 3 March 2005) is an Irish Thoroughbred racehorse and broodmare best known for her win in the Irish Oaks. Unraced as a two-year-old, her six-race track career lasted from April to October 2008. After finishing second in a maiden race on her debut she ran fourth in the Musidora Stakes and second in The Oaks before recording her first and only victory in the Irish Oaks. She finished unplaced in two subsequent races and was retired from racing at the end of the year. As a broodmare she has produced several good winners including US Army Ranger.