PURPOSE: To obtain the subject compound in high yield while suppressing the formation of by-product by carrying out the dehydrative imidation of an N- substituted maleinamic acid in the presence of a tin-based catalyst while supplying maleic anhydride to the system.

CONSTITUTION: An N-substituted maleimide is produced by using metallic tin or a compound containing tin element as a catalyst and carrying out the dehydrative imidation of an N-substituted maleinamic acid in a mixed solvent consisting of an organic solvent forming an azeotropic mixture with water (preferably xylenes) and an organic aprotic polar solvent (e.g. DMF or DMSO) while removing the formed water by azeotropic distillation. The dehydrative imidation reaction is carried out while adding 0.02-1.0mol of maleic anhydride based on 1mol of the amino group of the prim. amine used in the synthesis of the N-substituted maleinamic acid.