Abstract: Preparation of Ti doped Nb₂O₅ thin films on Al₂O₃ substrate by ion beam assisted deposition has been reported in this paper. The dependence of the oxygen sensitivity and structure of the film on its composition and annealing temperature has been examined. The resistance-oxygen partial pressure measurement shows that the oxygen sensitive characteristic of the pure Nb₂O₅ film is better than that of the pure TiO₂ film. A proper Ti doping in Nb₂O₅ film will improve its oxygen sensitivity and 5mol% Ti is optimal. An excessive Ti doping will degrade the oxygen sensitive characteristic markedly. A trace of Pt （0.3%-0.5%） added to 5mol% TiO₂-Nb₂O₅ film will not only increase its oxygen sensitivity but also reduce its response time. X-ray diffraction （XRD） spectrum and X-ray photoelectron spectrum （XPS） indicate that niobium oxide in TiO₂-Nb₂O₅ film is polycrystalline with monoclinic form while TiO₂ is in amorphous state and no change even for the composition up to 34mol% TiO₂. The pure TiO₂ film exists in the form of rutile structure. No obvious influence of different annealing temperatures （900-1100℃） on the film oxygen sensitivity and structure can be observed.