We describe the preparation of thin films of Ti-WO3 obtained by means of r.f. sputtering deposition followed by a thermal oxidation. The sensing characteristics of these thin films were obtained by measuring the response towards NO2 in the interval 0.5-20 ppm and to other interfering gases like ethyl alcohol, CH4 and CO; the influence of water vapour to the response towards NO2 was also investigated. The material seems to be a promising detector of NO2 for environmental monitoring.