(AB) star copolymers were prepared by crosslinking poly(styrene-b-isoprene) diblock anions with divinylbenzene. The microphase-separated structures of (AB)n star copolymers (arm number, n = 16, 16-19 wt% polyisoprene blocks) were formed with the dimensions of a unimolecular micelle in strong segregation. We carried out small-angle X-ray scattering measurements for (AB)n star copolymers in the form of dry film. These star copolymers formed the superlattice with a face-centred cubic structure in the bulk film.