N-Cyclohexylmaleimide having a cyclohexylaminosuccinic anhydride content of 0.001 to 1 wt. % is used as the main raw material for the production of heat-resistant resins. The resins are produced by a process of copolymerizing the above material with at least one monomer copolymerizable therewith which is characterized by the use of a monomer having a low yellowness, the addition of a compound which can inhibit the evaporation of the non-radical compounds contained in the monomer through reactions, the addition of an antioxidant, the use of a solvent containing alcohol, or the presence of a non-radical-polymerizable acid anhydride or carboxylic acid. The heat-resistant resins produced by the use of the above raw material or the above process are excellent in transparency, i.e., less discolorable, even when an increased amount of N-cyclohexylmaleimide is used for the purpose of imparting more excellent heat resistance. Accordingly, the heat-resistant resins can be suitably used in the fields necessitating both a low discolorability and a high heat resistance.