CdS has been proved to be an ideal material for use as the window layer for heterojunction solar cells especially with n-CdS/p-CdTe. CdS, Cd0.9Sn0.1S and Cd0.8Sn0.2S films were deposited onto glass substrates at 300 degrees C substrate temperature by using ultrasonic spray pyrolysis technique (USP). The effect of Sri concentration on some structural, optical and electrical properties of the films was presented. The crystal structure and orientation of the films were investigated by X-ray diffraction (XRD) patterns. XRD patterns showed that films have polycrystalline nature with a hexagonal structure. The grain size of the films decreased with increasing x values. The optical band gap values were obtained from optical absorption spectra of the films. The optical band gap values of the films were found to be between 2.44 and 2.45 eV. The variations of conductivity of Cd1-xSnxS (0 <= x <= 0.2) films have been investigated depending on applied voltage in dark and under illumination. The resistivity significantly decreased with increasing tin concentration and under illumination. (c) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.