For the purpose of the development of a skin-whitening agent, Sophora flavescens was evaluated for tyrosinase inhibitory activity and its active principles were identified following activity-guided isolation. The ethanol extract and dichloromethane fraction from S. flavescens showed significant inhibition of mushroom tyrosinase. From the dichloromethane fraction, three known prenylated flavonoids, sophoraflavanone G, kuraridin, and kurarinone, were isolated. Compared with kojic acid (IC(50)=20.5 microM), these compounds possessed more potent tyrosinase inhibitory activity. The IC(50) values were 6.6, 0.6, and 6.2 microM for sophoraflavanone G, kuraridin, and kurarinone, respectively.