With white kidney beans as raw materials, ultrasonic assisted extraction of proteins (α-AI crude extracts) was carried out and its process was optimized.Single factor and orthogonal experiments were carried out to determine the optimal conditions which were the solid to liquid ratio 1:10, the ultrasonic power 150 W, the extraction time 100 min, and the extraction temperature 55°C.Under these conditions, the protein extraction yield could reach 65.93%.On this basis, the α-AI crude extracts were separated and purified by organic membranes to obtain five components with different mol. weights, namely Z1 (>300 ku), Z2 (100∼300 ku), Z3 (50∼100 ku), Z4 (10∼50 ku) and Z5 (<10 ku).The protein content, mass proportion, extraction rate and α-amylase inhibitory activity of different components were determined and analyzed.The results showed that the protein content was in the order of Z4>Z3>Z2>Z1>Z5, and the corresponding mass proportions were 20.98%, 17.73%, 10.64%, 7.12% and 43.53%, resp.Within a certain concentration range, the α-amylase inhibitory rate was linearly pos. correlated with the concentrationThe α-amylase inhibitory activity was in the order of: Z4>Z3>crude extract>Z5>Z2>Z1, and the 50% inhibiting concentration (IC50) values of the corresponding components were 0.57, 1.35, 2.21, 3.44, 4.31, 6.09 mg/mL, resp.Among them, the extraction rate of Z4 component was 5.48%, while the IC50 was only 0.57 mg/mL, suggesting that it had a high extraction rate and better α-amylase inhibition activity, and obtained a good separation and purification effect.Ultrasonic combined with membrane separation is a better method for α-AI production