Abstract: To study the acute toxic effects of 180# fuel oil and dispersant on benthos, sea urchin (Glyptocidaris crenularis) was exposed to different concentrations (0.92 g/L、1.84 g/L and 3.68 g/L) of water-accommodated fractions (WAFs) and biological enhanced water-accommodated fractions (BEWAFs).The experiment included two parts:exposure period (24 h, 48 h and 96 h) and recovery period (24 h and 48 h).The effects of WAFs and BEWAFs on sea urchin were assessed by measuring the activities of CAT and SOD in gonad and intestines.The results showed that in the exposure period, the activities of CAT, SOD in gonad and CAT in intestines increased at first and then decreased, while the trends of SOD in intestines were increase-decrease-increase.The strong induction of CAT and SOD activities in intestines appeared earlier than that of gonad.And in recovery period, compared with gonad, the difference of CAT and SOD between intestinal tissue and control group was more significant.It indicated that intestinal tissue was more sensitive to petroleum hydrocarbon pollution than gonad.Compared with WAFs and BEWAFs, the changes of CAT and SOD in dispersant control group were not obvious, demonstrating subtle negative effects of bioremediation dispersant on marine organism, while the co-toxicity of dispersant and fuel oil was higher than that of WAFs.The activities of CAT and SOD were sensitive to petroleum hydrocarbon pollution and suitable for monitoring petroleum hydrocarbon pollution.