Synergetic inhibitory effect of genistein (I2) and D-glucose (I1) on alpha-glucosidase has been studied with kinetics method. It was concluded that the inhibitory effect was much greater when I2 and I1 were both added to the reactant solution simultaneously than that they were added, respectively, which suggesting the inhibitors bind to the different sites of alpha-glucosidase at the same time, and demonstrating synergetic inhibition.