The Prix Niel is a Group 2 flat horse race in France open to three-year-old thoroughbred colts and fillies. It is run at Longchamp over a distance of 2,400 metres (about 1½ miles), and it is scheduled to take place each year in September. The race serves as a trial for the Prix de l'Arc de Triomphe, which is held at the same venue three weeks later.