Cd1-xSnxS semiconductor films have been produced onto glass substrates at 573 K substrate temperature by the ultrasonic spray pyrolysis (USP) method using an aqueous solution with varying tin concentrations. The thicknesses of the films have been calculated to be in the range of 1-4 mu m. The films have been characterized to evaluate the structure, morphology, composition and optical energy band gap. X-ray diffraction (XRD) studies show that the films are polycrystalline with hexagonal, tetragonal and orthorhombic structures. The morphological and compositional properties of the films have been investigated using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Sn concentrations in the films have been varied from 0% to 84% as determined from energy dispersive analysis. The optical band gap energies and types of optical transition of the films have been determined from the optical transmittance spectra. The optical band gap energy values of the films decrease from 2.43 to 1.21 eV as the Sn concentration increases. (C) 2010 Elsevier B.V. All rights reserved.