Abstract: In order to elucidate the effects of heavy metal and polyaromatic hydrocarbons (PAHs) on the antioxidant enzyme activity and lipid peroxidation in marine polychaetes, cadmium (Cd) and benzo (a) pyrene (BaP) were selected as the representatives of heavy metal and PAHs respectively and the responses of antioxidant enzyme activities and lipid peroxidation in the polychate Perinereis aibuhitensis were studied when exposed to Cd, BaP and their combined pollution. Results showed that under Cd single pollution stress, there were no obvious dose-effect relationships between Cd concentration and the superoxide dismutase (SOD) as well as catalase (CAT) activities in P. aibuhitensis, while malondialdehyde (MDA) content increased with increasing exposed concentrations. Under BaP single pollution stress, SOD, CAT activities and MDA content were all strongly correlated with waterborne BaP levels. Under combined pollution of Cd and BaP, SOD activity of P. aibuhitensis was induced in the lower exposed concentrations and inhibited in the higher exposed concentrations, CAT activity, however, was inhibited in the lower exposed concentrations then returned to control level in the higher exposed concentrations. Meanwhile, MDA content was significantly induced only in higher exposed concentration. The current study suggests that Cd can interfere the influence of BaP on oxidation system in polychaetes and the combined exposure of the two pollutants made an antagonistic effect.