Early sexual maturation through temperature stimulation was induced in female and male of yezo scallop. Gonadosomatic index (GSI) in female showed 9.12 ¡¾ 2.9 in January, 14.89 ¡¾ 2.9 in February and 21.3 ¡¾ 1.4 in March in experiment¥°. GSI in experiment¥°showed a significant increase (P < 0.05) and in experiments ¥± and ¥² were not show significant variations (P > 0.05). It also showed significant between the control and the experiments ¥°, ¥±, and ¥² in February (P < 0.05) measurements. Experiment ¥° has showed good results in sexual maturation and spawning when compared with other experiments ¥± and ¥² and the control. Histological observation showed that ovary condition was in a growing stage in all the experiments ¥°, ¥±, and ¥². In February, ovary condition through histological observation was a late mature stage in all the experiments ¥°, ¥±, and ¥² except the control of a growing stage. GSI and gonad weight were 4.4 ¡¾ 0.88 and 2.8 g, respectively in November whereas it was 15.1 ¡¾ 2.8, and 11.7 g, respectively in January and 21.7 ¡¾ 5.4, and 19.4 g, respectively in February after rearing at a water bath of 12 ¡É depending on the condition of experiment I. It was possible early releasing of eggs and sperms of yezo scallop in February instead of the middle of April to the end of May being spawning period. Fertilized eggs have become a gastrula stage through a spiral cleavage and then become a trochophore larvae after 36 hours. After 10 days, D-shaped larvae have changed into an umbo stage larvae and attached to juveniles in the post larvae after 20-23 days.