Effects of the thickness of CdCl2 layer and the annealing on structural and optical properties of sputter-deposited US films were investigated. The annealing process of evaporated CdCl2 was carried out by heating the sample in air at 350-500 degrees C for 20 min. As the thickness of the CdCl2 increases, the (002) peak of CdS becomes weak and the other peaks of CdS increases. Especially, for 200 nm CdCl2 the preferential orientation of the (002) plane disappears and the c-axis of the CdS film tends to orient parallel to the substrate. As the CdCl2 layer is thicker, the grains are enlarged significantly. The improvement of optical properties of CdS films with thicker CdCl2 layer might be successfully employed in achieving better conversion efficiencies in solar cells. (C) 2007 Elsevier B.V All rights reserved.