Mar-Kell (1939–1966) was an American Champion Thoroughbred racehorse. Her dam was the 1934 American Champion Two-Year-Old Filly Nellie Flag, and her sire was the 1930 Epsom Derby winner Blenheim, who had been imported to the United States in 1937 by a syndicate that included Mar-Kell's breeder, Calumet Farm.