An epoxy resin composition according to the present invention comprises an epoxy compound (A), a block copolymer (B) and a curing agent (C), wherein the block copolymer (B) is composed of a polymer block (a) comprising a (meth)acrylic polymer and a polymer block (b) comprising an acrylic polymer that is different from the polymer block (a), said epoxy resin composition having such a property that a cured resin product produced by curing the epoxy resin composition forms a microphase-separated structure. A cured product of the epoxy resin composition forms a highly ordered phase structure, and therefore has excellent toughness and stiffness.