An epoxy resin was blended with a diallyl phthalate resin to improve the adhesive properties and the fracture toughness. A compatibilizer was used to reduce the decrease in heat resistance. An allyl ester compound [1,4-diallyloxycarbonyl-2,5-benzenedicarboxylic acid (DAPY)], which reacted with the diallyl phthalate resin and epoxy resin to have allyl groups and carboxylic acids on the end of the molecular chain, was synthesized as a compatibilizer by the reaction of pyromellitic dianhydride with allyl alcohol. These blends were cured with dicumyl peroxide and triethylamine. By modification with the epoxy resin and DAPY, the lap shear adhesive strength to steel increased up to about 3 times that of the diallyl phthalate resin. These results suggest that the secondary hydroxyl group generated by the addition reaction of the epoxy resin and DAPY and the secondary hydroxyl group existing in the molecular chain of the epoxy resin formed hydrogen bonds with the hydroxyl group of water existing on a metal surface, and as a result, the adhesive strength to metal such as steel increased. The fracture toughness of the diallyl phthalate resin was increased by modification with the epoxy resin. The reason for this result was that the flexibility increased because the crosslinking density became small by modification with the epoxy resin. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 913-919, 2010