The DPPH、·OH and ·O2-radical-scavenging activity and reducing power of α-amylase inhibitor obtained from crude extracts, ammonium sulfate precipitation, ion exchange chromatography and reversed phase liquid chromatography was studied. The results showed that the free radical scavenging capacity and reducing power of the α-amylase inhibitor not only increased with the increase of its concentration, but also increased with the increase of its purity in the reaction system within a certain concentration range.