Mercaptoacetic acid-modified CdS nanoparticles disperse selectively in the poly(4-vinylpyridine) domains of poly(styrene-b-4-vinylpyridine) (S4VP) block copolymer as a result of the formation of hydrogen bonds. This process in turn induces the morphological transformation of S4VP from a hexagonally packed cylinder structure into a lamellar structure, as evidenced from transmission electron microscopy, atomic force microscopy, and small-angle X-ray scattering studies. This transformation is consistent with that suggested by a theoretical prediction of the phase diagram of the mixed diblock copolymer/nanoparticle system.