Early sex differentiation of Chinese shrimp Penaeus chinensis was studied through scanning electronic microscope techniques and histological methods. The results showed that differentiation of external sex characteristics in P.chinensis began on the 35th day after the first stage of postlarvae, while sexual discrimination of the gonad through histological methods was possible for the first time on the 76th day after the first stage of postlarvae. This result indicates that sex manipulation should be done before the 35th day after the first day of postlarvae of Penaeus chinensis.