 O'Sullevan was also a racehorse owner, including of Be Friendly, who won the King's Stand Stakes at Ascot, and Prix de l'Abbaye de Longchamp.He was twice successful in the Haydock Sprint Cup (then Vernons Sprint) in 1966 and 1967.Another horse he owned was Attivo, whose victory in the 1974 Triumph Hurdle at the Cheltenham Festival was described by O'Sullevan as the most difficult race to call.