A seventy percent ethanol from mung bean (Vigna radiatae L.) was extracted further with CH(2)Cl(2), EtOAc and n-BuOH to afford four fractions: CH(2)Cl(2)-soluble, EtOAc-soluble, n-BuOH-soluble and residual extract fractions. When using l-3,4-dihydroxyphenylalanine as the substrate for mushroom tyrosinase, the EtOAc-soluble fractions showed the highest inhibitory activity. Two pure flavonoid compounds, vitexin and isovitexin, were isolated (using the enzyme assay-guided fractionation method) from the EtOAc-soluble fractions. Vitexin and isovitexin showed high inhibitory activities, with IC(50) values of 6.3 and 5.6 mg/ml, respectively. This is the first study on the active compositions of azuki beans against mushroom tyrosinase.