The CdS thin films were prepared by chemical bath deposition in a solution containing cadmium chloride,ammonium chloride,thiourea and ammonia.The morphological,structural and optical properties of CdS films were investigated by scanning electron microscope,X-ray diffraction and UV-vis-NIR spectroscopy.The photo-current response curves were also tested to study the optoelectrical performance of the films.It was found that uniform and compact CdS films could be prepared using pH values from 9 to 11.The CdS film prepared at pH=10 showed a most dense surface morphology and presented strongest peak intensities of the X-ray diffraction patterns and a band gap of about 2.37eV.According to photo-current response results,the CdS film with best quality has a highest photoconductivity of 2.94×10-2 Ω-1·cm-1 and a largest light and dark conductivity ratio of 38.23.