Abstract: We observed the shell length and survival between different coefficients of inbreeding to study the inbreeding depression for orange strain of Manila 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 (P < 0.05) 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 (12.05±6.54) %. 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 of Manila clam with orange shell color using the full-sib family.