Abstract: In order to evaluate the antioxidant activity of exopolysaccharides(EPS)which synthesized by Lactobacillus casei,the EPSs were isolated and purified from three L. casei strains(No. 3,5 and 7)with higher EPS production. Antioxidant activities(superoxide anion(O₂^-·),hydroxyl radical(·OH)and DPPH· radicals)of EPS were evaluated in vitro. Furthermore,the protective effect of EPS on H₂O₂-induced 293T cells oxidative injury was investigated. The results showed that EPS produced by the three strains had the highest scavenging rates when the EPS concentration was up to 400 μg/mL,and the scavenging rates were 8.87%(No. 5),88.94%(No. 7)and 34.55%(No. 7),respectively. The scavenging ability of hydroxyl free radical was better than that of ascorbic acid(65.87%). However,there was no significantly difference among the strains. Moreover,the EPS which was biosynthesized by L. paracasei No. 3 strain significantly raised the activities of superoxide dismutase(SOD)and total antioxidant capacity(T-AOC)and inhibited the formation of malondialdehyde(MDA)(P<0.05),which positively correlated with EPS concentration. The experimental results provide a basis for its use as an additive to enhance the antioxidant activity of food.