A process for the preparation of N-substituted maleimides by conducting heat-dehydration and dehydrating imidization of N-substituted maleamic acids under azeotropic distillation of generated water in a solvent mixture containing a solvent capable of forming water azeotrope and an organic aprotic polar solvent, in the presence as catalyst of a zinc salt of a maleamic acid, metallic zinc or a zinc compound which forms a zinc salt of the N-substituted maleamic acid in the reaction system.