The morphological structures of polystyrene-block-poly(ethylene oxide), PS-b-PEO, have been investigated under humidity controlled environments during film formation. Well-defined cylindrical microdomains oriented normal to the surface were induced by the high humidity during spin coating. Effects of the relative humidity (RH) on such ordered structures have also been studied. The results show that, the orientation and the ordering of the copolymer structures are very sensitive to the humidity of the environment during the film formation. Such ordered structure is stable at a variety of the RHs, and the phase contrast between the cylindrical PEO domains and the PS matrix domains can be significantly enhanced by the elevated RH. After the incorporation of the nanoparticles, however, the morphological structures of the PS-b-PEO are modified.