Tungsten trioxide (WO,) thin films were rf sputtered from a WO, target in various oxygen/argon (O-2/Ar) atmospheres and at different total pressures. A detailed structural and morphological investigation has been carried out on all obtained films by high resolution electron microscopy and nanodiffraction methods. Optical and electrical properties have been studied as function of deposition parameters. In addition, all obtained films were tested in controlled atmosphere in order to investigate their response to NO in the interval 2-100 ppm in dry air. The sputtering parameters were optimized in order to obtain the maximum sensitivity to NO gas. Finally, a close dependence between sputtering conditions, morphological features and physical properties was observed.