The effect of Ce3+ on the content of (reactive oxygen species ROS) in hepatocytes and V79 cells was studied with microfluorometry. The results showed that Ce3+ could enhance the concentration of ROS in hepatocytes in high dose and reduce the concentration of ROS in low dose. These results suggested that Ce3+ might decrease the damage of lipid peroxidation and DNA in low dose and might increase the damage of lipid peroxidaion and DNA in high dose.