Abstract: Acute toxic effects of benzene,toluene,o-xylene,m-xylene and p-xylene on Haliotis discus hannai were investigated using the semi-static bioassay.LC₅₀ values of the five chemicals acting on Haliotis discus hannai at 24 h,48 h,72 h and 96 h were obtained.The results indicated that there were significant positive correlations between the toxic effects on Haliotis discus hannai and the concentrations of the five chemicals in aquatic environment.The 96 h LC₅₀ values of benzene,toluene,o-xylene,m-xylene and p-xylene were 33.37,25.24,15.61,12.84 and 4.81 mg·L^-1,respectively,which suggesting that these five chemicals were all highly toxic to Haliotis discus hannai and the toxicity was in the sequence of p-xylene > m-xylene > o-xylene > toluene > benzene.