Abstract: In order to study the toxicity of phoxim on rats, and explore the role of oxidative stress in the mechanism of phoxim intoxication, phoxim was administrated intragastrically to SD rats with the concentrations of 30 and 300 μmol/kg body weight. After 15 and 30 days, the content of malondialdehyde (MDA) and the activity of cholinesterase（ChE）,superoxide dismutase（SOD）,glutathione peroxidase（GSH-Px）in liver tissue and plasma were determined and histopathological changes were detected. Results showed that activity of ChE in the plasma and liver were sighificant lower than that in the control group（P＜0.01）. Especially , the activity of ChE in high dosage group decreased to 22％ in plasma and 75％ in liver compared to the control. The activity of SOD and GSH-Px both decreased in plasma, the content of MDA increased in plasma and liver along with the exposed time extended Histopathological changes showed that fatty degeneration in hepatocytes of rats. The results indicated that phoxim can induce enhanced lipid peroxidation on SD rats and lesions of structure in the liver. The oxidative stress plays an important role in the mechanism of hepatotoxicity