Gonadal development, gametogenesis, reproductive cycle, gonad index, and flesh weight rate of the murex shell (Ocenebra japonica) collected from the rocky intertidal zone of Buan-gun, Jeollabuk-do, Korea were investigated by means of histological method from January to December 2002. O. japonica had separate sexes, and was oviparous. The gonad was widely situated on the surface of the digestive gland located in the rear of the spiral flesh part in the shell. The male penis was located near the two tentacles. The ovary was composed of a n㎛ber of oogenic follicles, and the testis was composed of several spermatogenic tubules. The size of ripe oocyte was approximately 140 ㎛ in diameter. The gonad index (GI) began to increase in March (33.24±2.33) and reached the maximum in June (47.77±1.90). Thereafter, the values decreased from July (45.12±3.60) to October (19.32±2.91). The flesh weight rate (FWR) began to increase in January (25.93±1.32) and reached the maximum in May (31.78±1.09). Thereafter, the values decreased from June (31.50±0.66) to October (24.09±1.60). The reproductive cycle could be classified into five successive stages: early active (October to April), late active (January to June), ripe (May to September), spawning (July to September) and recovery (September to February). The reproductive cycle was closely related to the seawater temperature.