Novel epoxy-based blends containing 30 wt % star styrene-b-butadiene block copolymers epoxidized at several degrees (SepB) have been investigated in order to analyze the effect of epoxidation degree on the ability of these copolymers to produce nanostructures inside the epoxy matrix as well as their effect on the network structure of the matrix. For neat styrene−butadiene (SB) and SepB15-modified systems, macroscopic phase separation was observed. The SepB epoxidized at 40−76 mol %, however, yielded hexagonally ordered nanostructures formed by PS cylinders arranged in the matrix containing also the epoxidized and nonepoxidized butadiene units. DSC analysis indicates that the slight differences observed in self-assembling of the mixture containing the 40 wt % epoxidized block copolymer with respect to those for the blends with higher epoxidation degrees could be related with reactivity differences of the epoxidized copolymers with the curing agent. It is envisaged that these novel nanostructured blends may lead to novel materials with excellent optical properties and enhanced fracture toughness.