Abstract: This paper deals with the gonadal development of Tilapia nilotica. In Hunan, the age of sex maturity of Tilapia nilotica which grows in the pond is 110—130 days; the male spawners ripen 20 days earlier than the female ones generally. The entire course of spermatogenesis as well as oogenesis, from spermatogonium to spermatozoon and oogonium to egg, can be completed endogenously in the pond environment. The oocytes develop from phase Ⅲ to phase Ⅳ non-synchronously. The histological structure of the ovaries return to stage Ⅳ after natural spawning or after natural degeneration, which testifies that female Tilapia nilotica spawns many times in a year.According to our research, there is nomicropyle and micropylar cell in the structure of a primary oocyte (phase Ⅳ), which is different from the primary oocyte of the grass carp and snail carp. The testes of male Tilapia nilotica are hermaphroditic mosaics at early stages of development.