rude extract prepared from white kidney beans (Phaseolus vulgaris) showed α-amylase inhibitory activity. Four fractions showed α-amylase inhibitory activity after the extract was subjected to reverse phase chromatography. The fraction with the highest activity was isolated and characterized. It was found to be a glycoprotein with an N-glycosylation site whose deglycosylated molecular weight is 54,847 as determined by electrospray ionization mass spectrometry (ESI-MS). Its C-terminal residues were serine, followed by alanine and tyrosine. Its binding constant was 2.8 μM at 55°C. The carbohydrate moiety was not involved in binding as its removal did not decrease the binding constant. Physiological amounts of kidney homogenate, plasma proteases, pronase or thermolysin readily hydrolysed the purified inhibitor; however, it was resistant to pepsin. Chloride ions were found to be important for full activity while calcium increased the initial rate of binding. Magnesium or sulfate ions did not have an effect on inhibition. Classical competitive inhibition of α-amylase was observed at pH 6.9.