PURPOSE: To obtain a heat-resistant polyester improved in resistance to hydrolysis or aminolysis at high temperatures, by reacting a polyester comprising an aromatic dicarboxylic acid and a glycol component with a difunctional polyester.

CONSTITUTION: A polyester comprising an aromatic dicarboxylic acid with a 2W6C glycol component is reacted with 0.1W5wt% diepoxy compound of the formula (wherein R is an organic group having a benzene ring) to decrease the content of the terminal carboxyl group to 15g-equivalent/106g polymer or below. Examples of the diepoxy compound include N,N-diglycidylbenzylamine and N,N- diglycidyl-2,6-dimethylaniline. These compounds can be synthesized by using a compound of the formula: RNH2 as a starting material and substituting hydrogen atoms on the nitrogen atom of the compound with glycidyl groups.