PbS thin films were deposited on glass slide substrates using the chemical bath deposition technique. The films were obtained in a reaction bath at temperatures of 10, 15, 20, 25 and 30 degreesC. The structure and surface morphology of the films were studied by X-ray diffraction and by atomic force microscopy measurements. The optical properties were determined from spectroscopy measurements of ellipsometry, transmission and reflection, in the energy range of 240-840 nm. In order to analyze the ellipsometry measurements, two models for the dielectric function of the films were considered, the Bruggeman's effective medium approximation and the Lorentz oscillator expression. From this analysis, the complex dielectric function epsilon(E) = epsilon(1)(E) + iepsilon(2)(E), thickness, roughness and void fraction of the films were examined as a function of temperature deposition. With the model obtained in the ellipsometry analysis, the optical spectra of reflection and transmission were calculated and compared with the measured spectra finding a good agreement. (C) 2003 Elsevier B.V All rights reserved.