Abstract: In this study,the effects of four kinds of soluble dietary fibers(barley β-glucan(BBG),xanthan gum(XG),konjac glucomannan(KGM),and tamarind seed polysaccharide(TSP))on the digestion of corn starch(CS)were studied by simulating human gastrointestinal digestion. In addition,by establishing the relationships between the viscosities of soluble dietary fibers and predicted glycemic index(pGI),the mechanisms by which soluble dietary fibers reduce the postprandial glycemic response were explored. The results showed that inhibition rates of supplementation of CS with 0.1% BBG,XG,KGM and TSP on the hydrolysis of starch by 11.59%,35.90%,30.54% and 19.62%,respectively,and reduced the pGI value of starch by 12.05,45.54,38.90 and 15.00,respectively. In addition,with the increase of the apparent viscosities of soluble dietary fibers in the gastrointestinal system,the pGI values showed a decreasing trend,and the downward trends of pGI values became more gradual when the apparent viscosities of XG,KGM and TSP were more than 4 mPa·s.In conclusion,soluble dietary fibers could inhibit the digestion of CS,and their viscosities are important factors to reduce the postprandial glucose response. This study would lay a theoretical foundation for the applications of soluble dietary fibers in reducing the blood glucose level.