Abstract: Fossils of three species of Equus are known in the Gulongshan Cave Site at Dalian, i.e. E. hemionus (the wild ass), E. przewalskyi sinensis (the small wild horse) and E. dalianensis (the large wild horse) Though the small wild horse is close to the living species E. przewalskyi in size of the body and metapodials, their upper and lower cheek teeth are smaller than those in the living species E. przewalskyi. These characters can distinguish the small wild horse from the living species E. przewalskyi. Therefore the small wild horse was tentatively named E. przewalskyi sinensis in 1990. We have recently observed the enamel structure of the cheek teeth of E. przewalskyi sinensis, E. dalianensis. E. hemionus, and the living species (E. przewalskyi caballus and E. hemionus) with Scanning Electron Microscope (SEM). This paper reports the result of a SEM study of the enamel structure of the equid forms mentioned above.