Sequential changes in body weight and oocyte development after injection of gonadotropic hormones were examined for wild Japanese Sea Bass collected during spawning season in 1991 and 1992. Just before hormonal treatment oocyte samples were sucked out with a catheter and maturational stage of oocytes was examined by microscopic and histological observations. Twenty mature females (3.7 to 5.9 kg) in 1991 and 13 females (2.3 to 7.2 kg) in 1992 spawning seasons, collected by longlines near the coast of Kujukuri in Chiba Prefecture, were used. They were injected with both human chorionic gonadotropin (HCG) and chum salmon pituitary extract (CP). Based on changes in the fish body weight and maturational stage of oocytes, artificial inseminations were conducted. The period from injection to ovulation varied depending on maturational stage of oocyte at the time of injection: 3-4 days needed from oocytes at the secondary yolk globule stage (oocyte diameter ranged 560-700 μm), 2-3 days from oocytes at the tertiary yolk globule stage (690-800 μm), 2 days from oocytes at the migratory nucleus stage (800-880 μm), 1 day from prematuration and mature stages (890-1080 μm and 1100-1190 μm). The present results combined with previous results suggest that time at which optimum egg quality is achieved is within one day after ovulation and optimum hormonal doses/kg fish are ca. 500 IU of HCG and ca. 20 mg of CP.