Novel mesoporous tungsten trioxide (WO3) films were deposited on ITO-glass by continuous, cathodic electrodeposition. The electrolytes for the deposition were prepared by using the peroxy-tungstic acid (50 mM) in 50:50 water: 2-propanol solution with varying amounts of sulfuric acid. It is observed that the morphology of the films could be controlled by varying the sulfuric acid concentration in the electrolytes. The most porous films were obtained at a pH of 0.8, and this had a thickness of 0.6 mu m, average particle size of 12 nm, and was quasi-transparent. The surface morphology and the structure of the films were characterized by X-ray diffraction, SEM, TEM, and cyclic voltammetry for the hydrogen intercalation reaction. Using a chopped light source, the present mesoporous WO3 films generated a photocurrent that was three times higher than transparent films. (c) 2005 Elsevier B.V. All rights reserved.