The Thousand Guineas Prelude, registered as the Tranquil Star Stakes is a Melbourne Racing Club Group 2 Thoroughbred horse race, for three year old fillies, at set weights with penalties, over a distance of 1400 metres, held annually at Caulfield Racecourse, Melbourne, Australia in late September. Total prize money for the race is A$200,000. This event is a preparation race for the prestigious Group 1 The Thousand Guineas later in October at Caulfield.