The role of superoxide and lipid peroxidation for anti-tumor effect of intra-arterial injection with degradable starch microspheres (DSM) was investigated in rabbits. The anti-tumor effect of intra-arterial injection with DSM was studied in rabbits with VX2 carcinoma of the hind leg. The tumor growth in rabbit treated with DSM 5 times was completely suppressed, and thiobarbituric acid (TBA)-reactive substances in the tumor tissue treated with DSM were significantly increased. But the anti-tumor effect of DSM and the increase in TBA reactive substances in the tumor tissue treated with DSM were significantly inhibited by treatment with superoxide dismutase combined with catalase. These results suggest that the anti-tumor effect of intra-arterial injection with DSM may be due to ischemia-reperfusion injury and that active oxygen species and lipid peroxidation may play an important role in the anti-tumor effect of intra-arterial injection with DSM.