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This present study aimed to investigate the effects of inbreeding on growth traits and genetic diversity in the swimming crab, Portunus trituberculatus. To this end, full-sibling inbred groups were established at four levels of inbreeding coefficient ( F values of 0.25, 0.375, 0.5, and 0.5937). The growth traits of the control group ( F ≈ 0) differed significantly from each of the inbred groups at three ages (80, 100 and 120 days old). Significant inbreeding depression was found in all inbred groups ( P < 0.05) and this ranged from −2.55 to −21.75 %, and there was a tendency for inbreeding depression to increase with increasing F value and age. At 120 days old, inbreeding depression was 7.6, 15.30, 16.89 and 21.75 % for the F values of 0.25, 0.375, 0.50 and 0.5937, respectively. Moreover, there was a tendency for inbreeding depression of body weight to increase with the increasing age; for example, inbreeding depression was greater at 120 days compared to that of 80 and 100 days old. Inbreeding depression per 10 % increase in the inbreeding coefficient value ranged from −1.02 to −4.08 %. The genetic parameter (e.g., PIC, n, a, Ho and He values) decreases with the increasing level of inbreeding. The greatest changes in the various genetic results are between the control group and the group ( F = 0.25), thereafter the rate of loss slows. This present study demonstrates that inbreeding has negative effects on growth traits and genetic diversity in P. trituberculatus, thus strengthening the case to maximize genetic diversity in selective breeding programs. [ABSTRACT FROM AUTHOR]