We attempted to improve the breed of red sea bream Pagrus major by means of selective breeding in order to establish red sea bream seedling for aquaculture capable of growing more quickly than natural red sea bream. In about 1964, natural young fish were reared into broodstock and, among young fish obtained from these broodstock, those growing quickly were selected and reared into broodstock. This selective breeding has been repeatedly carried out for more than 25 years. The following results were obtained. (1) As the selective breeding was repeated, the body weight of broodstock aged 4 years showed an increase. (2) The selected red sea bream seedling grew at an obviously elevated rate as the selective breeding was repeated. Namely, the time (days) required for attaining a commercially available fish size (about 1kg) was shortened. (3) The average realized heritability, which was determined by the average body weight of 4-year-old broodstock and body weight of 4-year-old fish in the growth curve of each generation, was 0.33±0.28.