Poly(4-vinylpyridine) core-polystyrene shell type polymer microspheres were synthesized by crosslinking the poly(4-vinylpyridine) spherical microdomains of poly(styrene-b-4-vinylpyridine) diblock copolymer films with 1,4-dibromobutane. The film formation of such core-shell type microspheres is investigated through small-angle X-ray scattering and electron microscopy. These microspheres formed a lattice with a body-centered cubic structure near the overlap concentration. In the bulk of the film, this structure changed to a face-centered cubic lattice.