Cadmium sulphide (CdS) thin films of different thicknesses were prepared by the chemical bath deposition technique (CBD) onto well-cleaned glass substrates at 80 degrees C from two chemical baths of different pH values 10 and 11. The thickness of the deposited films has been determined by gravimetry technique. The structural characterization was carried out by X-ray diffraction (XRD) and scanning electron microscopic (SEM) studies. These studies confirm the polycrystalline nature of the deposited films with hexagonal structure. The structural parameters such as lattice constants, crystallite size, dislocation density and number of crystallites per unit area have been evaluated. The composition of the various constituents in US thin films has been determined by energy dispersive X-ray analysis (EDAX). The optical properties have been studied in the range of wavelength 400-2500 nm and the optical transition has been found to be direct and allowed. The optical band gap values of US thin films of different thicknesses have been estimated and reported in this paper. It has been found that the films prepared from chemical bath of pH value 10 have better structural and optical properties than the films from bath of pH value 11. (c) 2005 Elsevier B.V. All rights reserved.