Abstract: An α-amylase inhibitor (α-AI) was isolated from white kidney beans (Phaseolus vulgaris. L) by ethanol fractional precipitation, ion exchange chromatography and gel filtration column chromatography. It was a homogeneity glycoprotein demonstrated by SDS-PAGE and gel filtration on CL-6B. The glycoprotein contained 88.2% protein and was rich in aspartic acid, glutamic acid, leucine, threonine and serine. The carbohydrate moiety was consisted of Man, Glc, Gal and Xyl in a mole ratio of 2.42∶1.50∶1.52∶1.00. The glycan and the core protein backbone was connected by O-linkage as determined by β-elimination reaction. The continuous oral administration of the α-AI (150 mg·kg^-1·d^-1 ) for 7 days can lower fasting blood glucose and 300 mg·kg^-1 ·d^-1 α-AI for 7 days can improve the sugar tolerance on alloxan-dependent diabetic model rats. The result showed the α-AI obtained from white kidney beans had good hypoglycemic effect on alloxan induced diabetic rats and may have high potential pharmaceutical value as a regulative digestive-starch degradation in patients suffering from diabetes.