Nellie Flag (1932–1953) was an American Thoroughbred racehorse who was retrospectively named the American Champion Two-Year-Old Filly of 1934.^[1] She was the first horse bred by Warren Wright's Calumet Farm to win a stakes race.^[2]

An early favorite, Nellie Flag finished fourth in the 1935 Kentucky Derby^[3] and seventh in the Preakness Stakes, the latter a race won by her dam in 1924.^[4] Following an injury, Nellie Flag was retired in mid July 1935 ^[5] and stood at Calumet Farm as a broodmare where she died in 1953 at age twenty-one. She produced ten foals of which nine raced.^[6] Among her best were:

• Mar-Kell (born 1939) - American Champion Older Female Horse (1943)
• Nellie L. (born 1940) - won 1943 Kentucky Oaks, Acorn Stakes
• Sunshine Nell (born 1948) - multiple stakes wins including Barbara Fritchie Handicap, Autumn Days Handicap, Top Flight Handicap

• Nellie Flag's pedigree and partial racing stats