The antioxidant activity and liver protective effect of Morus bombycis Koidzumi were investigated. Aqueous extracts of M. bombycis Koidzumi had higher superoxide radical scavenging activity than other types of extracts. The aqueous extract at a dose of 100 mg/kg showed significant hepato protective activity when compared with that of a standard agent. The biochemical results were confirmed by histological observations indicating that M. bombycis Koidzumi extract together with CCl4 treatment decreased ballooning degeneration. The water extract recovered the CCl4-induced liver injury and showed antioxidant effects in assays of FeCl2-ascorbic acid-induced lipid peroxidation in rats. Based on these results, we Suggest that the hepatoprotective effect of the M. bombycis Koidzumi extract is related to its antioxidative activity. (c) 2005 Elsevier Inc. All rights reserved.