Rivulus gaucheri, new species, is described on the basis of 11 specimens collected from small tributaries of the Litany river basin in the southwest highlands of French Guiana. R. gaucheri differs from all other congeners by the lack of the supracaudal spot at all ages in both sexes, a short base of dorsal fin, a yellow colour background of the body, a red colored sub-distal area on the anal fin in male, and a yellow one in female, and a dark margin of caudal fin.