Well aligned ZnO nanowire arrays are fabricated by a simple vapor phase transport process. Field-emission scanning electron microscopy shows the nanorods have a uniform length of about 1 um with diameters of 100 nm. After modified by ZnS, ZnO/ZnS core/shell nanowire arrays are formed and the thickness of ZnS layer increase with the increase of treatment time. X-ray diffraction analysis confirms that the as-synthesized ZnO nanorods are c-axis orientated, the modification of ZnS shell induces weak ZnS (100) diffraction peak for the treatment time of 180 min. The effects of shell thickness as a function of ZnS treatment time on the Raman scattering properties are studied. The results suggest that the coating of ZnS shell will change the Raman energy position and intensity of the ZnO nanowires, crystal lattice expansion and reconstruction of the ZnO/ZnS interface are responsible for the observed changes.