The species richness of the flat wasp fauna from Cousine Island, Seychelles, is reported for the first time. Three species are represented on this island in the Seychelles archipelago. The male of the previously described Seychelles species, Goniozus kiefferi Gordh is redescribed and its genitalia described and illustrated for the first time; the Oriental species Megasprosternum cleonarovorum Gupta and Azevedo, previously known from India, is recorded for the first time from the Seychelles and the Afrotropical region; and Holepyris gaigherae sp. nov. is described and illustrated. The Seychelles flat wasp fauna is now represented by nine species in total recorded from Cousine, Mahé and Silhouette islands.