Polycrystalline WO3 thin films were produced by spray pyrolysis on corning glass or ITO coated glass substrates. The optical, electrical and structural properties of these films were studied as a function of preparation conditions in their colored state. The transmittance value decreased from 80% to 5% when the films were colored. This was accompanied by an increase of the reflectivity in the NIR region. In addition, the electrical conductivity varied with heat treatment temperature. The change in electrical conductivity indicates that WO3 films exhibit a semiconducting behavior in their colored state. Furthermore, a change in the structure of the films from monoclinic to cubic was observed upon coloration. The electrochemical behavior was investigated in 1 M H2SO4/H2O solution using a three-electrode cell. (C) 2002 Elsevier Science B.V. All rights reserved.