High-quality and well-reproducible PbSnS3 thin films have been prepared by a simple and inexpensive chemical-bath deposition method from an aqueous medium, using thioacetamide as a sulphide ion source. X-ray diffraction analysis of the deposited films revealed that the as-deposited films were amorphous, however, an amorphous-to-crystalline phase transition was observed as the result of thermal annealing at 425 K for 1 h. The X-ray structure analysis of the collected powder from the bath annealed at 425 K for 1.5 h revealed an orthorhombic phase. Analysis of the optical absorption data of crystalline PbSnS3 films revealed that both direct. and indirect optical transitions exist in the photon energy range 1.24-2.48 eV with optical band gaps of 1.68 and 1.42 eV, respectively. However, a forbidden direct optical transition with a band gap value of 1.038 eV dominates at low energy (<1.24eV). The refractive index changes from 3.38 to 2.16 in.the range 500-1300 nm. The high frequency dielectric constant and the carrier concentration to the effective mass ratio calculated from the refractive, respectively. The temperature dependence of the electrical resistivity of the index analysis were found to be 4.79 and 2.3 x 10(20) cm(-3) deposited films follows the semiconductor behaviour with extrinsic and intrinsic conduction. The determined activation energies range are 0.35-0.42 and 0.76-85 eV, respectively. (C) 2003 Published by Elsevier Science B.V.