A 70% ethanol extract from azuki beans (Vigna angularis) 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. The EtOAc-soluble fractions showed the highest alpha-glucosidase inhibitory activity. Two pure flavonoid compounds, vitexin and isovitexin, were isolated (using the enzyme assay-guide fractionation method) from the EtOAc-soluble fractions. We further evaluated the interaction between the flavonoid compounds and alpha-glucosidase by fluorescence spectroscopy. Vitexin and isovitexin showed high inhibitory activities, with IC(50) values of 0.4 mg.mL(-1) and 4.8 mg.mL(-1), respectively. This is the first study of the active compositions of azuki beans against alpha-glucosidase.