We investigated the reproductive cycle with gonadal development of the female Cyclina sinensis by histological observations and seasonal changes in biochemical components of the adductor muscle and visceral mass tissues were studied by biochemical analysis, from January to December, 2001. The reproductive cycle of this species can be classified into five successive stages: early active stage (February to April), late active stage (March to June), ripe stage (May to August), partially spawned stage (July to October) and spent/inactive stage (September to February). Total protein contents in the adductor muscle tissues reached the maximum in February (early active stage) and appeared the minimum in June (ripe stage), while their contents in the visceral mass tissues reached the maximum in the late active and ripe stages (June) and gradually decreased from July (partially spawned stage) to November (spent/inactive stage). Changes in total protein contents showed a negative correlationship between the adductor muscle and visceral mass tissues (r = -0.499, p = 0.099). Total lipid contents in the adductor muscle tissues reached the maximum in January (the inactive stages) and their contents gradually decreased from February. Their contents in the visceral mass tissues, however, reached the maximum in June (late active and ripe stage) and gradually decreased from July (the partially spawned stage). On the whole, total lipid contents showed a negative correlationship between the adductor muscle and visceral mass tissues (r = -0.631, p < 0.05). Therefore, These results indicate that the nutrient contents of the adductor muscle and visceral muscle tissues change in response to gonadal energy needs. Glycogen contents in the adductor muscle tissue reached the maximum in March (early and late active stages) and decreased from July to September (partially spawned stage). while their contents in the visceral mass tissues reached the maximum in June (late active and ripe stages) and gradually decreased from July (partially spawned stage). Thereafter, their levels gradually increased in November (spent/inactive stage). On the whole, changes in glycogen contents appeared negative correlationship between the adductor muscle and visceral mass tissues. However, they showed no significant different (r = -0.307, p = 0.331).