A novel class of hydroxycoumarin derivatives were found to be potent α-glucosidase inhibitors. Their syntheses were reported and the structure-activity relationship was established. Kinetic enzymatic assays indicated that compound 10 was a slow-binding and noncompetitive inhibitor with a Ki value of 589 nM, while compound 11 was a competitive inhibitor with a Ki value of 4.810 μM. Among all hydroxycoumarin derivatives studied, compounds 10 and 11 exhibited the highest activities, were specific inhibitors of α-glucosidase, and could be exploited as the lead compounds for the development of potent α-glucosidase inhibitors. Compounds 10 and 11 were also selected for further discussion for the mechanism of enzymatic inhibition.