PURPOSE: Titled composition which can be completely cured by irradiating with light or a radiation and heating, comprising an epoxy resin, a polyfunctional carboxylic acid anhydride, a compound which , when irradiated with a radiation or light, generates a Lewis acid, and a quat. ammonium salt of a Lewis acid.

CONSTITUTION: A curable resin composition comprising (A) an epoxy resin containing at least two epoxy groups in the molecule, (B) a polyfunctional carboxylic acid anhydride copolymerizable with resin A, e.g., methyltetrahydrophthalic anhydride, (C) a compound which, when irradiated with light or a radiation, generates a Lewis acid, e.g., diaryliodonium salt of a Lewis acid of formula I, wherein M is a transition metal, B, P, As or the like, X is a halogen, n and m are integers, R1 and R2 are each nitro, OH, aryl or the like, and (D) a quat. ammonium salt of a Lewis acid, e.g., compound of formula II, wherein M, X, m and n are as defined above, and Z1WZ4 are each an alkyl, a halogen, phenyl or the like. As it is cured by irradiation with light or a radiation, the resin composition does not exude during heat curing and forms sag- or void-free products.