Growth of highly transparent and hydrophilic ZnS thin films on flexible polymeric and glass substrates has been performed using an environmentally friendly chemical bath deposition method with an ammonia and thioacetamide free reaction solution. Deposition time effect on surface morphology, structure and optical properties of the ZnS thin films has been investigated by field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffractometer (XRD), ultraviolet-visible light (UV-vis) spectroscopy, and photoluminescence (PL) spectroscopy. Also, the chemical composition of the prepared films has been studied in detail by energy-dispersive X-ray spectrometer (EDX), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. TEM images show that the ZnS films consisted of small nanocrystals with diameters <= 5 nm. Moreover, the water contact angles, 38.5 degrees and 25.4 degrees for ZnS films deposited on PS and on glass substrates, respectively, indicate a highly hydrophilic nature. Undoubtedly, the chemical analysis shows the formation of the films with a chemical composition of ZnS0.89, lacking impurities such as ZnO and/or Zn (OH)(2). Additionally, FE-SEM images show a homogenous deposition over a very large surface area substrates. Ultimately, the obtained photoluminescence spectrum indicates a strong and broad emission peak ranging from 400 to 600 nm, which are due to deep levels or trap state defects in the crystalline structure of the ZnS films.