PURPOSE: To provide an epoxy resin compsn. for improving the flexibility of not only epihalohydrin-bisphenol type but also novolac and cycloaliphatic type of epoxy resins.

CONSTITUTION: An epoxy resin compsn. is prepared by blending 95 to 5 pts.wt. of (a) an epoxy resin having one or more epoxy groups in the molecule with 5 to 95 pts.wt. of (b) an epoxy-modified block copolymer comprising a polymer block (A) consisting mainly of a vinyl aromatic compd. and a polymer block (B) consisting mainly of a conjugated diene compd. or a partly hydrogenated diene compd. The resultant epoxy resin compsn. can be cured with a commonly used hardener such as acid anhydride, aliphatic amine, aromatic amine, novolac phenol and dicyan-diamide to form a cured product with high flexibility.