Abstract: The effects of ten natural extracts (including bitter melon,buckwheat,pumpkin and so on) on blood glucose lowering were evaluated by iodine colorimetric method and p-nitrophenyl-β-D-galactopyranoside (PNPG) method.The combination of natural extracts with the starch of other grains was also investigated by UV-Vis absorption spectrum method.The results showed that the inhibitory effects of bitter gourd on α-amylase and α-glucosidase activity were better than those of other nine plant extracts,while the inhibition rates were 64.12% and 67.69%,respectively,indicating that bitter gourd extract had higher efficiency on blood sugar lowering.The combination of natural material extract with starch of grains will produce copolymer precipitation and reduce its inhibitory activity on carbohydrate digestive enzymes.The results of UV-Vis absorption spectra scanning ranged from 300 to 350 nm showed that a large amount of copolymer precipitation was formed when bitter gourd extract combined with rice,glutinous rice and glutinous rice.In contrast,bitter gourd extract had weaker binding effect with corn starch.Therefore,corn starch can be used as a raw material for developing low glycemic index foods for glycemic control of diabetic patients.