CdS, ZnO and ZnO/CdS core-shell nanorod films were prepared by chemical bath deposition. The samples were characterised by UV-Vis spectroscopy and scanning electron microscopy. The results show that the norder ZnO nanorods have been etched in the alkaline solution, at the same time, CdS was deposited on the ZnO surface. Effect of the concentration of OH- on the optical prosperties of CdS films were investigated by the optical transmission spectra. The results show that the transmission decrease with the increasing of the concentration of OH- due to increasing of the film thicknees, which can be ascribed to the increasing of S2+ concentration. The mechanisms of the forming of ZnO/CdS core-shell nanorods film in the alkaline solution were further analyzed.