PURPOSE: To provide an epoxy resin compsn. which has good storage stability, does not cause deformation due to shrinkage during curing and gives a cured article having excellent mechanical and electrical characteristics, by blending a specified glycidyl ester of a polycarboxylic acid as a reactive flexibilizer.

CONSTITUTION: A glycidyl ester of a polycarboxylic acid of formula I (wherein R is a group of formula II, III or IV) such as diglycidyl 7,11-octadecadiene-1,18-dicarboxylate, diglycidyl 6-vinyl-8-hexadecene-1,16-dicarboxylate or diglycidyl 7,8- dihydroxytetradecane-1,14-dicarboxylate is used as a reactive flexibilizer. 5W 400pts.wt. said flexibilizer and a hardener such as hexahydrophthalic anhydride are blended with 100pts.wt. epoxy resin such as Epikote 828 (a product of shell chemicals).