Tranquil (1920 – October 1938) was a British Thoroughbred racehorse and broodmare. She showed considerable promise as a two-year-old when she won one race and finished second in the Gimcrack Stakes. In the following season she was one of the best horses in Britain, scoring classic victories in the 1000 Guineas and St Leger Stakes as well as winning four other races including the Jockey Club Cup and Newmarket Oaks. he won once in 1924 before her racing career was ended by injury. She made no impact as a broodmare.