Amphibian populations appear to be declining around the world. Although there is no single cause, one factor may be pollution from heavy metals. Heavy metals such as cadmium (Cd) have been one of the most fundamental causes of soil and water pollution in industrial and developing countries. The liver and kidneys are the main target organs for toxic effects of Cd. We used the frog Rana nigromaculata as a test subject to evaluate the effect of Cd on oxidative stress and antioxidative ability under a long-term exposure. Female frogs were exposed to 12.5 and 25.0 mg/L of cadmium dissolved in water for 30 days in experiment condition. The concentration of cadmium, levels of malondialdehyde (MDA), the contents of glutathione (GSH) and the activities of superoxide dismutase(SOD) in the liver and kidneys were determined at the end of the 10th, 20th and 30th days of Cd exposure respectively. The results showed that the cadmium accumulation and the MDA contents in the liver and kidneys were increased rapidly with the prolonged time at the dosage of 12.5 and 25.0 mg/L Cd, and Cd accumulation was strongly positive correlated with the MDA contents in the liver (R²=0.8643, n=9). GSH contents were induced significantly in the liver and were decreased significantly in the kidneys with increasing of exposure time, GSH contents were positively correlated with MDA contents in the liver (R²=0.5933, n=9), while GSH contents were negatively correlated with MDA contents in the kidneys (R²=0.8609, n=9). SOD activities in liver were increased in the dosage of 12.5 and 25.0 mg/L Cd and SOD activities in the kidneys were first raised and declined afterwards in the dosage of 25.0 mg/L Cd with increasing of exposure time. These results suggest that the enhancement of peroxidation of membrane lipid may be one of the cadmium injury mechanisms in R. nigromaculata. Furthermore, the increasing of GSH content and SOD activity would be part of general defense strategies to cope with oxidative stress.