Nanocrystalline ZnS films have been prepared on glass and quartz substrates by sulfurizing the as-sputtered ZnO films at 500 ° C in H2S or sulfur-vapor. The films are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive analysis of X-ray (EDX) and UV-visible transmission spectra. It is found that the total conversion of ZnO films in sulfur-vapor to the hexagonal ZnS films requires 11 h much longer than that in H2S, due to the low S content in sulfur-vapor. And the high ZnS (0 0 2) preferred orientation can be observed for ZnS films formed in H2S or low pressure sulfur-vapor. The results also show that ZnS films formed in sulfur-vapor have about 200 nm grains greater than those formed in H2S, because the solid-phase recrystallization during the sulfidation process is favorable in sulfur-vapor. Besides, the great broadening of the absorption edge in the optical transmission spectra, and the small band-gap energies compared to that of ZnS films formed in H2S, are obtained for ZnS films produced in sulfur-vapor, which can arise from existence of some ZnO and residual sulfur phase, and sulfur interstitial atoms in the films. © 2004 Elsevier B.V. All rights reserved.