The present study examined the inhibitory effect of aqueous extract from the gall of Rhus chinensis (AEGRC) on alpha-glucosidase activity, an enzyme responsible for digestion of carbohydrate to monosaccharides in the process of intestinal absorption. AEGRC inhibited Bacillus alpha-glucosidase acitvity with an IC(50) of 0.9 micro g/ml. Its inhibition on alpha-glucosidase was determined to be noncompetitive and reversible when the enzyme-substrate mixture was simultaneously treated with AEGRC as an inhibitor. In addition, when it was orally administered to rats with sucrose (2g/kg), AEGRC (250-1000mg/kg) significantly suppressed the increase of blood glucose levels after sucrose loading in a dose dependent manner. These results suggest that AEGRC might exert anti-diabetic effect by suppressing carbohydrate absorption from intestine, and thereby reducing the postprandial increase of blood glucose.