We report a systematic study on preparation and morphological observation of hybrids composed of a block copolymer and hydroxy-capped semiconductor nanoparticles via hydrogen bonding. Three polystyrene-b-poly(4-vinylpyridine) (PS-P4VP) block copolymers with exactly the same PS chain length but with different P4VP chain length were synthesized via reversible addition fragmentation chain transfer polymerization. To prepare hybrids, each PS-P4VP was mixed with hydroxy-capped nanoparticles made of cadmium selenide (h-CdSe), by varying a weight ratio of PS-P4VP:h-CdSe. Morphology of three series of hybrids was observed by both transmission electron microscopy and small-angle X-ray scattering. Hybrids composed of h-CdSe and PS-P4VP bearing a long P4VP block represents uniform morphology of a single nanophase-separated structure, where domain spacing expansion and morphology transition induced by addition of h-CdSe were observed. On the other hand, nonuniform morphology, i.e., macrophase separation accompanied by overflow of h-CdSe from nanophase-separated domains, was observed in hybrids containing PS-P4VP bearing a short P4VP block. These results are attributed to hydrogen-bonding formation and the stoichiometric balance of functional groups.