Zinc sulfide thin films (0.20 mu m) were prepared on silicon and polycrystalline alpha-Al2O3 substrates by hydrothermal treatment of zinc sulfide sol in the temperature range of 100-200 degrees C for 6-24 h. The films prepared were found to have a cubic structure and the film deposited on Si(111) has a {111} preferred orientation. The films were characterized by X-ray diffraction, scanning electron microscopy and infrared transmission spectrum.