The antioxidative effect of cellulose, wheat bran and pectin was studied in rats. Wistar rats (40) were randomly divided into 4 groups, 3 groups were fed with the fibers at a level of 10% in weight, the 4th group consumed stock food as control. After 3 months' feeding, MDA in serum and in RBC membrane of the 3 treated groups were significantly lower than that of the control group. The RBC membrane fluidity was significantly increased. It is suggested that these three kinds of dietary fibers can reduce the level of lipid peroxidation and inhabit free radical injury to RBC membrane in rats.