|Annual reproductive cycle of Siganus canaliculatus was studied based on monthly variation of gonadosomatic index (GSI) and histological changes of gonads. Samples were monthly collected by a set net along the southern coast of Jeju Island, Korea from January to December, 1996. Variation of the monthly mean GSI values showed similar trends in female and male. The GSI values increased from June and reached a peak in the spawning season in July (9.65±1.96 in females, 10.00±4.27 in males), and decreased rapidly thereafter. Female hepatosomatic index (HSI) values ranged from 1.26±0.22 (in April) to 2.34±0.39 (in July), and male HSI values ranged from 1.27±0.21 (in April) to 1.87±0.30 (in October). Annual reproductive cycle was classified into the following successive stages: in female, growing stage (from February to June), mature stage (from June to July), ripe and spawning stage (from July to August), recovery stage (from August to March); and in male, growing stage (from January to June), mature stage (from June to July), ripe and spent stage (from July to August), and recovery stage (from August to April). Based on these data, this species has a group-synchronous oocyte development and one spawning season a year.