The biological effects of the water extracts of Rhus Verniciflua Stokes (RVS) were evaluated by protection against hydroxyl radicals. Antioxidative activities were measured using both 1,1-diphenyl-2-picrylhydrazyl (DPPH) and thiocyanate method. Also we used the Glucose oxidase (GO) 20 mU/$ extrm{m}{ell}$ hydroxyl radical generating system in mouse forebrain cell culture. Water was used for ex-traction from RVS as a solvent which has high polarity especially. In DPPH method, the antioxidative activities of the crude water extract were stronger than any other extracts of low polar-solvents. In the antioxidative effects of mouse forebrain culture using 20 mU/$ extrm{m}{ell}$ GO, cell viabilities were evaluated 65.6%, 68.8% at 1 $mu extrm{g}$. 5 $mu extrm{g}$ addition of crude water extracts (30 mg/$ extrm{m}{ell}$) respectively. 10 $mu extrm{g}$ addition of crude water extracts had more than 86.1% cell viabilities, P<0.0l significantly, compared with the group treated with GO alone. In comparison with the antioxidative activities of several commercial antioxidants (ascorbic acid, $alpha$-tocopherol, catalase, serum), 273 $mu extrm{g}$/$ extrm{m}{ell}$ addition of crude water extracts (300 $mu extrm{g}$/$ extrm{m}{ell}$) showed equivalent antioxidative effect to 25 uM ascorbic acid.