PURPOSE: To obtain the titled resin, by adding a rubbery polymer to a vinylaromatic compound, bulk-polymerizing the mixture in the presence of an unsaturated dicarboxylic acid anhydride and effecting both suspension polymerization and ring-closing reaction in the presence of an unsaturated dicarboxylic acid half ester.

CONSTITUTION: A rubbery polymer (e.g., polybutadiene) is dissolved in a vinylaromatic compound monomer (e.g., styrene) and the solution is bulk-polymerized while an unsaturated dicarboxylic acid anhydride (e.g., maleic anhydride) is being added continuously. Then, the polymerization mixture is suspension-polymerized in the presence of an unsaturated dicarboxylic acid half ester (e.g., n-butyl monomaleate). Then, the purpose heat-resistant, impact-resistant resin is obtained by effecting an alcohol-eliminating ring closure reaction of the unsaturated dicarboxylic acid half ester under vacuum and heating. The weight ratio of the total unsaturated dicarboxylic acid anhydride to the vinylaromatic compound monomer is preferably about 65W95:35W5.