This study attempts to propose the possibility of the sex reversal in Sinonovacula constricta and Gomphinaveneriformis by confirming the changes in the sex ratio with the shell length in the same population level. For analysis of sexratio, 100 individuals of S. constricta (SL 26.5~95.0 mm) and 2385 individuals of G. veneriformis (SL 15.1~60.1 mm) wereused. Sex was analyzed histologically. Both species displayed the tendency of increase in the female proportion with increasein shell length. In this study, changes in the sex ratio in accordance with the growth of S. constricta and G. veneriformis aredetermined to be indirect evidence that signifies their sex reversal.