Abstract: We observed the shell length and survival between different coefficients of inbreedingto study the inbreeding depression for orange strain ofManila clam (Ruditapes philippinarum) through experiments. Four experimental groups were established, including first generation of half-sib (H1, F=0.125), first generation of full-sib (F1, F=0.250), fourth generation of full-sib (F4, F=0.594) and the control group (C1, F=0). The results show that the shell length of F1 is smaller than that of other groups at larval, juvenile, and grow-out stages. One-way ANOVA indicates that the difference in shell length is significant (P0.05) between F1 and other groups at juvenile and grow-out stages, and that there are no significant differences among H1, F4 and C1. The growth rate of shell length in F1 decreases significantly, with a inbreeding depression rate ranging from 2.92% to 18.33%, of which the mean value is (12.056.54) %. Shell length in H1 has a depression at juvenile and grow-out stages as well. However, there is no inbreeding depression of length in F4 at any stages. There are no inbreeding depression of survival for H1, F1 and F4 , as of which the survival rates are higher than that of control group C1. The results in this study suggest a basic theory to select the strain ofManila clam with orange shell color using the full-sib family.