A large series of lens were collected from normal and senile cataractous human eyes, and were investigated according to the theories of oxyradical and lipid peroxide (LPO). The findings showed that the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase in the senile cataractous lens were very significantly lower than those in the normal ones, while the content of malondialdehyde (MDA) in the lens of senile cataractous eyes was very significantly higher than that of normal eyes. The results suggest that the oxyradical and LPO might be one of the direct causes leading to senile cataract formation.