Oxidative stress has been recognized as a critical pathogenetic mechanism for the initiation and the progression of hepatic injury in a variety of liver disorders. Antioxidants, including many natural compounds or extracts, have been used to cope with liver disorders. The present study was designed to investigate the hepatoprotective effects of cassia seed ethanol extract (CSE) in carbon tetrachloride (CCl(4))-induced liver injury in mice. The animals were pre-treated with different doses of CSE (0.5, 1.0, 2.0 g/kg body weight) or distilled water for 5 days, then were injected intraperitoneally with CCl(4) (0.1% in corn oil, v/v, 20 ml/kg body weight), and sacrificed at 16 hours after CCl(4) exposure. The serum aminotransferase activities, histopathological changes, hepatic and mitochondrial antioxidant indexes, and cytochrome P450 2E1 (CYP2E1) activities were examined. Consistent with previous studies, acute CCl(4) administration caused great lesion to the liver, shown by the elevation of the serum aminotransferase activities, mitochondria membrane permeability transition (MPT), and the ballooning degeneration of hepatocytes. However, these adverse effects were all significantly inhibited by CSE pretreatment. CCl(4)-induced decrease of the CYP2E1 activity was dose-dependently inhibited by CSE pretreatment. Furthermore, CSE dramatically decreased the hepatic and mitochondrial malondialdehyde (MDA) levels, increased the hepatic and mitochondrial glutathione (GSH) levels, and restored the activities of superoxide dismutase (SOD), glutathione reductase (GR), and glutathione S-transferase (GST). These results suggested that CSE could protect mice against CCl(4)-induced liver injury via enhancement of the antioxidant capacity.