In this research, the effect of Fe2O3 content on the electrochromic properties of WO3 in thermally evaporated (WO3)(1-x)-(Fe2O3)(x) thin films (0 <= x <= 0.4) has been studied. The atomic composition of the deposited metal oxides was determined by X-ray photoelectron spectroscopy analysis. The surface morphology of the thin films has been examined by atomic force microscopy. The surface roughness of all the films was measured about 1.3 nm with an average lateral grain size of 30 nm showing a smooth and nanostructured surface. The electrochromic properties of (WO3)(1-x)-(Fe2O3)(x) thin films deposited on ITO/glass substrate were studied in a LiClO4 + PC electrolyte by using ultraviolet-visible spectrophotometry. It was shown that increasing the Fe2O3 content leads to reduction of the optical density (Delta OD) of the colored films and also leads to increasing the optimum coloring voltage from 4 to 6 V in which Delta OD shows its maximum values, in our experimental conditions. Furthermore, by using this procedure, it is possible to make an electrochromical filter which behaves similar to the colored WO3 film in the visible region, while it can be nearly transparent for near-infrared wavelengths, in contrast of the pure colored WO3 film. (c) 2005 Elsevier B.V. All rights reserved.