Fractionation with supercritical CO(2) is employed to divide ethanolic extract (E) of B. kaoi into four fractions (R, F1, F2 and F3). To assess the selectivity of the fractionation, extracts of the four fractions were characterized in terms of the hepatoprotective capacity and activity of antioxidant enzymes to against CCl(4)-induced damage. The in vitro study revealed that pretreatment with B. kaoi extract or its fractions, except F3, significantly protected primary hepatocytes against damage by CCl(4) (P<0.05). The R and F1 fractions had the highest saikosaponins content (175 and 200 mg/g dry weight, respectively) and most effectively protected the liver from damage by CCl(4). This study demonstrated that the oral pretreatment of B. kaoi (100 and 500 mg/kg), except F3, three days before a single dose of CCl(4) (CCl(4)/olive oil=1:1, 3 ml/kg, sc) was administered significantly lowered the serum levels of hepatic enzyme markers (AST and ALT) (P<0.05). A pathological examination showed that lesions, including ballooning degeneration, necrosis, hepatitis and portal triaditis were partially healed by treatment with B. kaoi extract and fractions. Oxidative stress induced by CCl(4) led to lipid peroxidation (MDA) and changes in the levels of the antioxidant enzymes in the liver. However, all the fractions, except F3, markedly suppressed lipid peroxidation and reversed the activities of the antioxidant enzymes to the normal levels.