A world-wide concern for enviromental safety that demands monitoring the emission of hazardous gases into the atmosphere, combined with recent advances in wireless senzor networks is increasing the need of low-power gas sensors and low-cost. Among metal oxides, between theirselves the tungsten oxides are among the most used materials in electro-, photo- and gasochromic applications. In this work, a soft chemical nanocrystalline processing route has been demonstrated for the preparation of hexagonal tungsten oxides by the acidic precipitation of Na2WO4.2H2O solution at temperatures as low as 120 °C and 330 °C. The structural properties of films were investigated by TEM Philips CM-20. The sensing properties of films were measured to gaseous ammonia at various temperatures. We founded the correlation between structure and gas sensing properties of WO3 films. The average size of WO3.1/3 H2O crystallites is ~ 50 ÷ 100 nm. After the head treatment of films, the average size of WO3 crystallites decreased to ~ 30 ÷ 50 nm. The electron diffraction of the film confirmed the phase change from orthorhombic to hexagonal one. The gas measurements were performed by direct injection using a gas serynge, and the arrows in the graphics indicate the total amount of gas present in the measurement chamber after successive injections.