PURPOSE: To prepare a heat-resistant resin inexpensively and stably by a resource-saving process, useful for producing a film or a coating compound, etc., by reacting a polyfunctional carboxylic acid containing an acid anhydride group with a hydroxyl group-containing compound, reacting the reaction product with a poly-functional isocyanate.

CONSTITUTION: In an organic solvent (N-methyl-2-pyrrolidone, etc.), a polyfunctional carboxylic acid (e.g., trimellitic anhydride, pyro-mellitic anhydride, etc.) containing one or more acid anhydride groups in one molecule is reacted with a compound (e.g., methanol, i-propanol, etc.) containing one or more hydroxyl groups in one molecule. The reaction product is then reacted with a polyfunctional isocyanate (diphenylmethane-4,4'-diisocyanate, etc.) having two or more isocyanate groups in one molecule, and, if necessary, a polyfunctional carboxylic acid having one or more acid anhydride groups in one molecule and/or a polyfunctional carboxylic acid having two or more carboxyl groups in one molecule, to give a heat-resistant resin.