Abstract: We observed and determined the sagittae morphology of 105 individuals of genus Decapterus (Decapterus macrosoma, D. tabl and D. kurroides) collected from the Dongsha Islands in the South China Sea. The sagittae shape of genus Decapterus was long oval with developed rostrum, and the difference between species was distinct. The front end of D. macrosoma rostrum was slightly bent downward. The knob of otolith dorsal of D. tabl was obviously developed with serrated shape, and the front end of rostrum was slightly broad and thick. The overall outline of D. kurroides otolith was smoother, and antirostrum was poorly developed. According to the morphological indices (otolith length, otolith width, rostrum length, rostrum width, otolith mass and otolith area), the classification of different species of genus Decapterus (D. macrosoma, D. tabl and D. kurroides) achieved success rates of 100%, 100% and 91.7%, respectively. It is shown that sagittae can identify genus Decapterus.