The hydrogen gas sensing performance of platinum (Pt) catalyst activated tungsten trioxide (WO3) thin films were investigated in the present study. The WO3 thin films exhibited a gasochromic effect; i.e., a reversible change in color from transparent when in air to blue when in hydrogen (H-2). All processes proceeded rapidly at room temperature. The films were prepared by the electrodeposition method under ambient conditions. A layer of Pt was then sputtered onto the surface of WO3 film. The cycling of the coloration was obtained from UV-Vis spectra. The Pt catalyst dissociated H-2 into H atoms, which then diffused into the WO3 thin film, which transformed from WO3 to (HxW1-xWxO3)-W-Vt-O-V and changed the color of the WO3 thin film. Therefore, we could detect the existence of H-2 by the coloration of the WO3 thin film. Sensor properties of WO3/Pt films were investigated at room temperature in H-2-N-2 gas mixtures containing 0-50 mol% of H-2. The results show that the transmittance change (Delta T) of the electrodeposited WO3 hydrogen sensor was similar to 2% when the concentration of H-2 was 5 mol%, and similar to 20% when the concentration of H-2 was 50 mol%. Coloration and bleaching had good response and recovery times in the range of 5-60 s, respectively. (C) 2007 Elsevier B.V. All rights reserved.