Abstract: Kudzu root starch was hydrolysed by mid-temperature α-amylase and assisted by ultrasonic. Based on single factor tests, a series of Box-Benhnken design experiments were used to determine the optimal hydrolysis process parameters by taking dextrose equivalent (DE) as standard. The optimal ultrasonic conditions were showed at ultrasonic power 90W for 10min. Under these conditions, the optimum enzymolysis process conditions were as follows:solids concentration 29.6%, hydrolysis for 32min, enzyme concentration 1.19%. Scanning electron microscope images showed that Kudzu root starch granules had an irregular flaky shape after hydrolysis, and the surface became loose, thus more apt to dissolving in water.