Thin films of BiVO4 with monoclinic structure were deposited onto indium-doped tin oxide (ITO)-coated glass substrates by ultrasonic spray pyrolysis. The effects of tungsten doping and hydrogen reducing were investigated. The films were characterized with XRD, Raman spectra, SEM, UV-Vis transmittance spectra. Furthermore, the films were investigated by electrochemical and photoelectrochemical measurements with regard to splitting water for solar energy conversion. The films possessed a scheelite-monoclinic structure with good absorption to visible light. The optical band gaps were evaluated to be about 2.65 eV. The flat band potentials were estimated to be about -0.61 V vs. saturated calomel electrode (SCE) in 0.5 M Na2SO4 solution from Mott-Schottky plots. For non-doping samples, the incident photon to current conversion efficiency (IPCE) was relative low because of low density and activity of carriers. When treated with hydrogen reducing, the carrier density increased due to more oxygen vacancies, resulting in the increase of IPCE. In addition, substituting 1% vanadium with equal mole tungsten can increase IPCE remarkably, which achieved about 10% at 0.3 V vs. SCE potential under 400-450 nm wavelength photo irradiation. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.