The bioassay guided refractionation of the methanol extract of roots and rhizomes of Veratrum taliense (Liliaceae) yielded five stilbenoids: veraphenol, resveratrol, piceid, isorhapontin, and mulberroside E, all inhibiting xanthine oxidase (XO, EC 1.2.3.2.) in vitro in a dose-dependent manner with IC50 values of 11.0, 96.7, 66.1, 70.0, and 78.4 microM, respectively. Veraphenol and mulberroside E were found to be mixed XO inhibitors with the Ki and Ki data of the former being 32.8 and 239.3 microM, and those of latter 32.5 and 13.8 microM, respectively. However, the inhibition on the enzyme by resveratrol, isorhapontin, and piceid was shown to be competitive with their Ki values of 9.7, 19.1, and 14.3 microM, respectively. Among the five stilbenoids, veraphenol and resveratrol were also revealed to inhibit competitively monoamine oxidase A (MAO, EC 1.4.3.4) with IC50 values at 38.0 and 26.6 microM, and Ki data 36.4 and 47.3 microM, respectively. However, none of the stilbenoids was inhibitory on MAO B in our assay. The structure-activity relationship examination showed that glycosylation of the stilbenoids could reduce the inhibition on XO and diminish the activity against MAO A, indicating that the free phenolic hydroxy group of the compounds was most likely essential for these bioactivities.