Abstract: When attacked by microbes,the immune system of the host can be activated,which induces many changes. One of them is that the hemocytes can produce reactive oxygen intermediate(ROIs)to kill the microbes. On the other hand,anti-oxidant system is necessary to maintain an appropriate amount of ROIs,and keep a good balance between killing microbes and protecting itself from hurt by superfluous ROls. Vitamin E(VE)and selenium(Se)are two important components of the anti-oxidant system,and can eliminate the superfluous ROIs directly or indirectly. In the present study,a two-factorial experiment was designed to evaluate the effects of dietary Se and VE on antioxidant enzyme activities,which can reflect the oxidant status of the organisms,abalone Haliotis discus hannai Ino. Totally eight semi-purified diets were formulated to provide graded levels of Se(0,0.2,0.6,1.5mg/kg)and VE(0,50IU/kg). Abalone of similar size(6—7cm)were distributed randomly into buckets with re-circulating sea water. Eight different artificial diets and one control(fresh kelp,Laminaria japonica)were tested. Each treatment had three replicates. The feeding experiments lasted for 120 days. The culture conditions during this period were as follows:12 hr illumination per day,water temperature 15.6—20.5℃,salinity 31—34,dissolved oxygen 7.2mg/L,pH 7.5—7.9. After the feeding experiments,the animals were sacrificed and hemolymph was withdrawn,and centrifuged at 3000 r/min for 5 min at 4℃. The supernatant was kept in -70℃ for further use. The activities of catalase(CAT),superoxide dismutase(SOD),glutathione peroxidase(GPX),glutathione reductase(GR),glutathion-S-transferase(GST)in serum were assayed. The results showed that dietary Se had more efficient effects on antioxidant enzyme activities than VE. Dietary Se had significant effects on all five antioxidant enzyme activities(P<0.05),while VE significantly influenced the activities of only GPX and GR(P<0.05). There were significant interactions between Se and VE on the activities of CAT,GPX and GR(P<0.05). It was found that SOD and CAT activity in abalone serum decrease with increasing of dietary content of Se or VE. GPX activity increased when dietary Se content increased. GST activity was the highest when no Se or VE in the diet. Addition to enzyme activities,GPX/SOD, GR/GPX and CAT/SOD ratios were used as indices of antioxidant level. It was found that these three ratios were affected significantly by dietary selenium(P<0.05),while only GR/GPX was influenced significantly by dietary VE. Se and VE had interaction in GPX/SOD and GR/GPX(P<0.05). When no Se or VE was added to the diet,the value of GR/GPX and CAT/SOD was the highest(2.3 and 0.3 respectively) while GPX/SOD was the lowest(0.6). These indices also changed sensitively when Se or VE were added. In the diet containing 0.6mg/kg Se,the GPX/SOD was the highest. When 0.6mg/kg Se and 50 IU/kg VE was added to the diet, GP/GPX reached the lowest point,and also the value of CAT/SOD showed the decreasing trend with Se and VE was added. Considering all the indices we had measured,it could be concluded that 0.6mg/kg Se and 50 IU/kg VE could keep the antioxidant enzymes in a balanced level,which could protect abalone from oxidant damages. According to these results,the abalone fed with kelp,L.japonica kept better antioxidant status at the end of the experiments than those fed with artificial diet.It indicated that the formula of the artificial diet used in the present experiments still needs to be optimized.