To study effects of heated oil on lipid peroxidation in rat liver, rats were fed 3 and 6 weeks by intubating oils heated for l1(HA group) and 24 hours (HB group) at 18$0^{circ}C$. The contents of lipid peroxides and vitamin E, and the activities of super oxide dismutase and glutathione peroxidase in liver were measured. Histological changes of the liver tissue were observed. In both HA and HE groups, the contents of lipid peroxides and the activities of superoxide dismutase were increased, but the activities of glutathione peroxidase and the contents of vitamin E in liver were decreased when compared to the control group which was fed fresh cora oils. During the oil feeding period, the activities of superoxide dismutase and the contents of vitamin E were not significantly changed, but the activities of glutathione peroxidase were decreased, and lipid peroxides were increased in the 3 weeks than in 6 weeks. In HB liver, the heterochromatin of nucleus increased, mitochondria swellen, cristae in mitochondria disappeared, fat droplet and secondary lysosome increased and lumen of rough endoplasmic reticulum enlarged, compared with that of the control group. These phenomena in HA group were less pronounced.