The objectives of this study were to investigate the characteristics and mechanism of gonad maturation including identified maturation inducing steroids and its physiological role in the final oocyte maturation (FOM) in yellowfin porgy. yellowfin porgy, Acanthopagrus latus are functional male for the first year of life but begin to change sex during the second year. Only 30~50% of cultured yellowfin porgy are change into females in 2-year-old, while 80% fish become females at 3-year-old. Vitellogenesis were observe between August and November and have the highest gonadosomatic index (GSI %) at 6.88 % and 14.35 % in 2 and 3-year-old female yellowfin porgy respectively. Highest serum levels of T occurred simultaneously during spawning season in one and two years of age in functional male, while highest level concentration E2 were observed at the same time in two and three years old female fish. GSI increased 1.5-fold during FOM and reach 2-fold at germinal vesicle breakdown stage (GVBD). Oogenesis in 3-year-old female yellowfin porgy was divided into three stages¡F(1) previtellogenic stage from February to July with the primary oocytes¡F(2) vitellogenic stage from August to October and with full growth oocyte of diameter at 400