Previously, a flavonoid fraction, which consisted mainly of protocatechuic acid, fustin, fisetin, sulfuretin, and butein, here named RCMF $({underline{R}}VS;{underline{c}}hloroform-{underline{m}}ethanol;{underline{f}}raction)$, was prepared from a crude acetone extract of Rhus verniciflua Stokes (RVS) which is traditionally used as a food additive and as an herbal medicine. In this study, we evaluated the effects of RCMF on the antioxidant defense system using embryonic normal hepatic cell line (BNL CL.2) and its SV40-mediated transformed cell line (BNL SV A.8). This study demonstrates that RCMF selectively stimulated the antioxidant defense system of normal cells, as BNL CL.2 cells proved to be more sensitive to RCMF-mediated increases of superoxide dismutase, catalase, glutathione, and glutathione reductase than BNL SV A.8 cells. In particular, RCMF caused a significant increase in the malonaldehyde content of BNL SV A.8 cells, which is believed to be closely associated with cytotoxicity of RCMF and RCMF-mediated growth inhibition. Collectively, our findings suggest that the flavonoid fraction, RCMF, selectively stimulates the antioxidant defense system in normal rather than hepatic tumor cells.