Advanced reactive gas deposition was used to produce pure and Auactivated nanocrystalline WO3 films for gas-sensing studies. Many different methods - such as X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive spectroscopy, scanning electron microscopy, and atomic force microscopy - were used to characterize structural properties of the films. The WO3 particles in the films had the high-temperature tetragonal crystal structure after deposition, and the average crystallite size was about 10nm. The effect of sintering on structural, electrical, and gassensing properties of both pure and Au-activated WO3 films was also studied. Gas response experiments with films on alumina substrate were done at different operation temperatures, from room temperature up to about 450°C, at exposure to different concentrations of H2S and H2 in dry synthetic air. © Physica Scripta 2004.