In this paper, we report the effect of deposition time on the properties of zinc sulfide thin films. The ZnS thin films have been grown on amorphous glass substrates and at various deposition periods ranging from 30 to 120 min by chemical bath deposition technique. Other parameters, such as reactant concentration, solution pH, and bath temperature were kept constant for the all depositions. Morphological characterizations of the surface were studied using the atomic force microscopy (AFM). The AFM images confirmed that the grain size of ZnS increased with increased deposition time. Average diameter of nanoparticles was between 60 and 90 nm, while the roughness ranged from 6 to 11 nm. Optical properties, which were determined from UV-VIS spectrophotometry, were obtained by analyzing the measured absorbance and transmittance spectrum. The zinc sulfide thin films show high transmittance in the visible region and the ZnS band gap value was estimated to be in range of 3.99 -4.05 eV.