In this study, the effect of humidity on the growth characteristics and properties of chemical bath-deposited ZnS thin films was systematically investigated. All deposition was conducted by an open CBD system under various relative humidity levels (RH) or by a hermetic CBD system as a comparison. It shows, for films deposited by an open system, the ambient humidity plays an important role in the quality of the resultant films. Damp environments lead to powdery films. Generally, all films prepared in this study using NH3 and hydrazine hydrate as the complexing agents were amorphous or poorly crystalline. For an open system, the [H+] from the dissolved carbon dioxide in the air competes with the ammonium ions in the bath solution. According to Le Chatelier's principle, more ammonia was consumed, which favors the free [Zn+2] in the solution, facilitating the homogeneous precipitation of Zn(OH)(2) and giving rise to a powdery film. The x-ray photoelectron spectrum shows, for an open system, the content of Zn-O compounds in the form of Zn(OH)(2) and ZnO, etc., is increased by the relative humidity of the environment. The visible transmittance is reduced by RH. The higher optical band gap of the as-deposited films could be attributed to the quantum confinement effects due to the small grain size of the polycrystalline ZnS films over the substrates. (c) 2014 Elsevier B.V. All rights reserved.