The ethanol extract of Rhus verniciflua S. was subsequently isolated and fractioned into two portions using H_2O and 99% ethanol as elution buffers through silica gel column chromatography. To study the antioxidative effect of Rhus verniciflua S. extracts, cultured hepatocytes were exposed to hydroxyl radical generated by 20 mU·ml^-1 glucose oxidase for 4 h in the presence or absence of water or ethanol eluted extracts. Addition of 100㎍·ml^-1 water extract to the culture medium protected from hydroxyl radical-mediated cytotoxicity of hepatocytes almost equivalently to the control. When the hepatocytes after culture for 24 h were incubated with 100㎍·ml^-1 water or ethanol extract without glucose oxidase for 4h, activity of catalase was increased by 1.40- and 1.31-fold, compared to the control, whereas with the commercial catalase (100 units·ml^-1) was 1.64-fold. These results show that in vitro both extracts has a potential reducing cytotoxicity effect on hydroxyl radical and enhancing activities of the cellassociated catalase in cultured hepatocytes. Apoptosis induced by 12-O-tetradecanoylphorbol 13-acetate (TPA, 100 nM) in mouse hepatocytes were blocked by the addition of 100㎍·ml^-1 of water or ethanol extract. In the biological effects of two extracts, water extract was more effective than that of ethanol extract.