Niobium-doped amorphous titanium oxide film can be deposited on a Corning glass substrate using a mixture of ammonium hexafluorotitanate, boric acid, niobium oxide and ammonium hydrogen fluoride aqueous solutions. After thermal annealing, the nanocrystallite niobium-doped titanium oxide film can be obtained. The smaller crystallite size of nanocrystallite niobium-doped titanium oxide than that of undoped-titanium oxide benefits the catalytic activity for sensing gas. A thin-film niobium-doped titanium oxide oxygen sensor with a higher sensitivity and a faster response is demonstrated.