Abstract: The SOD, CAT, AKP activities and MDA content were determined after Cyclina sinensis were exposed to different concentrations (2 mg·L^-1, 8 mg·L^-1 and 32 mg·L^-1) of naphthalene under experimental ecotoxicology conditions. The results indicate that C.sinensis had high mortality rate under 32 mg·L^-1 of naphthalene. Under non-lethal conditions and with increase of naphthalene exposure time, SOD activity showed a continuous increasing trend; CAT activity was promoted in low-concentration group and inhibited in high-concentration group; AKP activity was initially increasing then decreasing; MDA content fluctuated following the trend of low→high→low. According to Pearson correlation analysis, SOD and CAT showed synergistic effect (R=0.439, P < 0.01), while SOD and AKP showed antagonism effect (R=-0.571, P < 0.01). CAT and AKP might protect cellular membrane structure better than SOD (R=-0.490, P < 0.01).