Reproductive biology (sexual maturity and reproductive cycle) of starry flounder Platichthys stellatus were examined by histological methods. From March 2004 to February 2005, 144 females and males were sampled. Gonadosomatic index (GSI) of female and male were peaked in May and February, respectively. Monthly changes of hepatosomotic index (HSI) showed a negative correlationwith those of the GSI. Changes of condition factor (CF) in female were correlated with gonad maturation, while that of male were no difference all the year round. Based on monthly GSI and gonadal development the reproductive cycle of starry flounder could be divided into four stages: growing stage (September to November), maturation stage (September to February), ripe and spent stage (March to May), and recovery and resting stage (June to August). Biological minimum size of female was 1,074 g. The relationship between fecundity (F) and body weight (BW) of the fish was expressed as $F;=;455.86BW^{1.2006}$.