N-Cyclohexylmaleimide (CHMI) was synthesized in high yield by dehydration and ring closure of N-cyclohexylmaleamic acid (CHMA) in an organic nonpolar solvent that is immiscible with water in the presence of a catalyst consisting of a mixture of acid and its amine salt. The optimal molar ratio of the acid to the amine is in the range of 1/0.65-1/0.8. N-Cyclohexylaminosuccinic anhydride (CASA), which is a major by-product, was found to induce coloration of the methyl methacrylate/CHMI copolymer. The CASA content could be decreased by distillation under reduced pressure. CHMI contaminated with less than 0.9 wt % of CASA can be used for heat-resistant poly(methyl methacrylate) resin (MMA/CHMI copolymer) free from coloration, as well as for methyl methacrylate homopolymer.