Wide bandgap compound ZnS is one of the promising materials used in versatile applications including solar cells, UV photodetectors and luminescent devices. Compared to other II-VI sulfides, ZnS has several advantages of non-toxicity, wider solar spectrum transparency and earth-abundance. Recent progress on optimization of synthesis techniques of ZnS allows it to be effectively realized on transparent and flexible substrates. In this work, nanostructured ZnS films were deposited on bare quartz and ITO coated glass substrates using RF sputtering at various conditions. Crystal structural, optical and surface chemical properties of ZnS films have been systematically characterized. It is revealed that ZnS films exhibit cubic β-phase crystalline structures on both substrates. The optical transmittance of ZnS films is above 85% in the visible range. The substrate temperature plays an important role in crystalline quality of ZnS films. Sputtering power exhibits more effects on the thickness and optical properties of ZnS films. Optimization of deposition parameters has been realized by investigation of optical, microstructure and crystallinity of ZnS thin films in this study.