This study histologically describes the gonadal development and reproductive cycle of the abalone, Haliotis discus discus inhabiting Jeju island of Korea. Gonads displayed histologically definitive seasonal changes. The gonad index (GI) of both females and males was the highest (3.2 and 3.3) in September and was the lowest (1.7 and 1.4) in January and February. Egg diameter increase from early stage in March and reach about 180 μm to ripe stage in August. The condition index (CI) were highest in July and lowest in May. The pattern of changes in the GI. egg diameter and CI were similar to the pattern of seasonal changes in gonadal tissues. The female ratio (F/F + M) was 59% (n = 182:127). The reproductive cycle was divided into an inactive stage (January-February), early active stage (March-April), late active stage (May?July), ripe stage (August?October) and spent and degenerative stage (November-January). The main spawning period of Haliotis discus discus was August to October at Jeju island in 2014.