Abstract: The purpose of this study was to examine potential antidiabetic effects of plant polyphenols commonly found in foods. Inhibitors of the enzyme α-glucosidase have been shown to be useful as antidiabetic agents. Eleven naturally occurring compounds were tested for inhibitory activity with the enzyme α-glucosidase obtained from rat intestine using the substrate p-nitrophenyl-α-D-glucopyranoside (PNP-G). These compounds included 10 polyphenols, 4 of which are anthocyanidins and trans-cinnamic acid. Acarbose was used as the standard. Both total inhibition and kinetic measurements were made in this study. All of the anthocyanidins tested showed inhibitory activity. All polyphenols tested were active except for caffeic acid. trans-Cinnamic acid was also weakly active. Ferulic acid, rutin, cyanidin, malvidin and delphinidin showed competitive inhibition behavior. However, tannic acid and pelargonidin showed noncompetitive behavior. Quercetin and trans-cinnamic acid showed mixed inhibition behavior. All compounds containing at least one ether or glycosidic link show competitive behavior. Cyanidin, delphinidin and gallic acid do not have any ether or glycosidic links but still displayed competitive kinetic behavior. The relation between chemical structure and inhibitory activity of the compounds are discussed. In summary, the majority of the compounds tested showed significant α-glucosidase inhibitory activity. The type of inhibition varied between compounds. The mechanism of inhibition needs to be further explored.