To clarify the vasculotoxicity of reactive oxygen intermediate(ROI) in cultured vascular endotherial cells(VEC), of mouse, cytototoxicity was measured by MTS assay after VEC was incubated to 10～80mU/ml xanthine oxidase(XO) and hypoxanthine(HX) for 2 hours. and also, the protective effect of Radix Polygoni Multiflori(RPM) was determined by MTT assay in these cultrures. Cell viability was positively decreased dose-, and time-dependently, after the treatment with 40mU/ml XO/0.1 mM HX to cultured VEC for 2 hours. In the vasculoprotective effect of RPM on the toxicity induced by XO/HX, RPM prevented the XO/HX-induced cytotoxicity in these cultures. From above the results, it suggests that XO/HX is toxic in cultured VEC and herb extract, RPM has protective effect against the vasculotoxicity induced by XO/HX.