To provide a polymer alloy which is used as a structural material having excellent mechanical properties or a functional material having excellent regularity and has a disperse phase of a bimodal structure, at least a part of that can be controlled minutely, in which the bimodal structure is dispersed uniformly and which is composed of at least two resins.

In the polymer alloy composed of at least two thermoplastic resins, a vinyl monomer (A), which is a precursor of at least one thermoplastic resin, is subjected to a chemical reaction in the coexistence of the other thermoplastic resin (B1) and/or a precursor (B2) of the other thermoplastic resin to induce spinodal decomposition. As a result, the disperse phase of the polymer alloy has the bimodal structure and at least a part of the bimodal structure can be controlled minutely so that the polymer alloy in which the biomodal structure is uniformly dispersed can be obtained.