Amphibian populations appear to be declining around the globe.Among many reasons behind this, an important factor may be heavy metals pollution. Heavy metals such as cadmium (Cd) are one of the most fundamental causes of soil and water pollution in industrial and developing countries. The liver is the main target organ affected by Cd toxicity. We used the frog Rana nigromaculata as a test specimen to evaluate the oxidative stress and metallothionein (MT) content of liver under long-term exposure to toxic levels of Cd. Adult frogs were exposed to 10 mg?L-1 Cd in the form of CdCl2 in water for 4, 10, and 30 days. The Cd concentration along with metallothionein ( MT), glutathione (GSH) and malondialdehyde (MDA) contents in the liver were detected. The results indicated that Cd accumulation, GSH and MT contents in liver increased significantly in a time-dependent manner. MDA content in liver increased significantly compared with the control groups after 10 days treatment. These results suggest that Cd can induce hepatic oxidative damage, and the increasing of GSH and MT contents might be part of general defense strategies to cope with oxidative stress.