The one possibility of lowering postprandial glucose levels is by the inhibition of α-amylase activity. In this study, aqueous extracts from local Thai fruits were tested for their inhibitory effect on α-amylase. The results showed that the fruits of Kluai Hom Thong; Musa (AAA group) showed significant reduction in α-amylase activity. An α-amylase inhibitor was purified by using a combination of ammonium sulfate precipitation, ion exchange chromatography with DEAE cellulose, and gel filtration chromatography with Superdex 75, respectively.