Sixteen N-phenylphthalimide derivatives were synthesized and their ability to inhibit ${alpha}-glucosidase$ was investigated. N-(2,4-dinitrophenyl)phthalimide was a potent inhibitor of yeast ${alpha}-glucosidase;(IC_{50};;0.158{pm}0.005mM);and;maltase;(IC_{50};;0.051{pm}0.008mM)$, whereas it did not inhibit sucrase. From a Lineweaver-Burk plot of ${alpha}-glucosidase$ kinetics, N-(2,4-dichlorophenyl)phthalimide was found to be a competitive inhibitor of yeast ${alpha}-glucosidase$. These results indicate that N-(2,4-dinitrophenyl)phthalimide could be a representative of a new group of ${alpha}-glucosidase$ inhibitors.