The antioxidant action of Artemisia campestris was examined in vitro and in vivo. A water extract of A. campestris showed a strong scavenging action of 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl and superoxide anion radicals. When the extract was given intraperitoneally to mice prior to carbon tetrachloride (CCl4) treatment, CCl4-induced liver toxicity, as seen by an elevation of serum aspartate aminotransferase and alanine aminotransferase activities, was significantly reduced. Depression of the elevation of serum enzyme levels after CCl4-treatment was also observed by oral administration of the extract. In that case, CCl4-derived lipid peroxidation in the liver was decreased by the extract treatment. These results suggest that the extract of A. campestris scavenges radicals formed by CCl4 treatment resulting in protection against CCl4-induced liver toxicity.