This report describes the development, differentiation and maturation of the gonad in Tilapia mossambica. Through histological studies, mainly there are three stages canbe divided. 1. The newly hatched fry before the yolk sac is absorbed, there are only a fewprimordial germ cells observed at the root of coelomic membrane between themesonephric duct, dorsal aorta and the gut. 2. Sex remains undifferentiated 10 days after hatching,and when the fry attains 9mm in total length, the gonadal anlage usually differentiated into two types. The broadones develop more rapidly, and contain many germ cells, some of which show mitoticphase. The other is small and narrow, which contains only 2 or 3 germ cells without anymitotic phase. 3. At the stage of 30 days after hatching, when the fry attains to 25 mm in totallength, the germ cells of the large gonadal anlage enter into the early oocyte stage andfurther develop to form ovary. While the germ cells of the small gonadal anlage justbegin to enter the mitotic phase, they will develop into testis later. So that the differen-tiation of the testis is about 20 days later than that of the ovary. The ovary and thetestis mature at the stage of 90 days after hatching. For the purpose of sex inducement in Tilapia mossambica, it is suggested that theprocess is better to operate before the fry reaches to the length of 9 mm, and so thesuccess may be more reliable.