CdS buffer layers deposited by chemical bath deposition (CBD) have been used in high-efficiency Cu(In,Ga)Se2 (CIGS) solar cells. In view of the harmful environmental impact of Cd due to high amount of Cd compound waste from large scale solar cell production, Cd-free buffer layers should be developed. In this work CBD method was used to deposit nanocrystalline zinc sulfide (ZnS) thin films for CIGS solar cell. The growth behavior containing deposit morphology, growth rate, structure and optical properties of ZnS thin films within 100nm thick is investigated by a field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), atomic force microscope (AFM) and ultraviolet visible light spectroscope (UV/VIS). The FE-SEM morphologies showed that the impact, even and dense ZnS films were deposited on soda lime glass from solution contained high concentration ratio of thiourea. The TEM diffraction patterns and XRD patterns revealed that ZnS films were nanocrystallines, of which FCC (111) phase dominated. The growth rate and transmittance of ZnS thin films are 0.88nm/min and over 80%, respectively. The ZnS/CIGS/FTO structure and Al:ZnO/ZnO/ZnS structure in CIGS solar cell formed by wet processes showed good heterointerfaces.