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. Mar-Kell was bred in Kentucky and was raced by Calumet Farm for four years, from age two through five. Trained by future U.S. Racing Hall of Fame inductee Ben Jones, as a four-year-old, Mar-Kell was named American Champion Older Female Horse honors.