Abstract: A novel heat-resistant resin composition moldable in 20 to 180 seconds at a temperature of 130.degree. to 180.degree. C. and excellent in mechanical strengths at high temperatures is obtained by mixing a polyaminobismaleimide with a modifying reagent selected from the group consisting of (A) a diallyl phthalate prepolymer and (B) a mixture thereof with at least one monomer having a polymerizable double bond and 2 to 20 carbon atoms, and an organic peroxide. In this resin composition, the low mechanical strengths at high temperatures of phenolic resins and silicone resins, which are a drawback of these resins, and the unsatisfactory curability of an unmodified polyaminobismaleimide resin have been overcome. The present composition, therefore, is suitable for use in electrical parts, electronic parts, automobile parts, and machine parts.