Green Sunfish,Lepomis cyanellus,is a kind of small fresh-water fish introduced by Guangdong Province in 1997 from North America.Gonadal development of this species was studied by light microscopy.The developmental chronology of gonad is composed of 5 stages.At the age of 1 month,ovaries and testes were at stage Ⅰ,and both gonads developed to stage Ⅱ at the age of 2-3 months.Ovaries and testes developed to stage Ⅲ and stage Ⅳ respectively by 4 months and 5-6 months.The first maturity age was 7-8 months.During the winter,ovaries degenerated to stages Ⅱ-Ⅲ,and testes still stayed at stage Ⅴ.The maturation coefficient of matured ovaries was 2.80%-8.10%,and that of matured testes was 1.45%-3.45%.The development of ovaries and testes was asynchronous.This species spawn repeatedly and the spawning period lasts from March to November in Guangzhou region.The reason for this species' slow growth and the feasibility of L.cyanellus as an experimental model animal were discussed in this paper.