Blends based on epoxy resin and random copolymers, poly(styrene-co-allylalcohol) (PS-co-PA), were studied. Two PS-co-PA copolymers, with different hydroxyl content, and a polyallylalcohol (PA) homopolymer were used to analyze the effect of polyalcohol content. The polymers presented similar values of molar mass. The miscibility of noncured mixtures and the thermal transition behavior of cured blends were investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). Its morphology was studied using both scanning and transmission electron microscopy (SEM and TEM). While the epoxy/PA blends are homogenous materials, because of the epoxy/hydroxyl reaction, PS-co-PA/epoxy blends shows separated phases. In these blends, the presence of a third glass transition, whose value is an intermediate between those of pure components, and the presence of a well-defined interfacial layer between PS-co-PA domains and epoxy matrix indicates a secondary epoxy/hydroxyl reaction. The modification of epoxy resin with PS-co-PA provides significant increase in the storage modulus measured by DMTA.