The effects of inbreeding on growth and survival of Pacific oyster(Crassostrea gigas)were investigated using inbreeding families which were established by first generation of full-sib mating(F₁,F=0.250)and second successive generation of full-sib mating(F₂,F=0.375).Control group(F=0)was produced by random mating of wild oysters.The fertilized rate,hatching rate,survival rate,growth and inbreeding depression coefficients were compared between different experimental groups.The results indicated that all the three experimental groups had high fertilized rates ranging from 94.42% to 98.46%,and hatching rates were all above 90% except group F₂.The growth of F₁ and F₂ showed significant inbreeding depression after 12 days of breeding at larval stage.An increasing inbreeding depression of growth was observed with the increase of inbreeding coefficient in group F₁ and F₂ at post-larval stage.The inbreeding depression coefficient of average shell height was found to be -0.386 0% at F=0.250,-0.647 1% at F=0.375 at 20 d.The inbreeding depression of larval survival was obvious and increasing with age.The inbreeding depression coefficients of larval survival in group F₁ and F₂ ranged from -0.197 2% to -2.490 5% and -0.136 3% to -2.232 5%,respectively.A significant inbreeding depression in average shell height of spat was observed all the time in families with F=0.250 and F=0.375.Inbreeding depression of shell height of group F₂ was higher than group F₁ at juvenile stage.However,no significant difference of average shell length of spat was found between control group and the other two inbreeding groups.Inbreeding depression of survival existed all the time in inbreeding families with F=0.250 and F=0.375 at juvenile stage,and both of them increasing with age.This study demonstrates that inbreeding has negative effects on the economic traits,especially on growth and survival.These effects even still exist in the family with second successive generation of full-sib mating,thus it is necessary to highlight the importance to maximize the genetic diversity in selective breeding programs.These results also emphasize the significance of maintaining pedigree records which are used to avoid the deleterious effects of inbreeding depression in shellfish breeding programs.