Achievement of nanosized thin films of titania was achieved by radio-frequency sputtering of a Ti(97%)–Mo(3%) target. Deposition was performed under inert or reactive atmosphere followed by annealing at temperatures up to 800 °C. The resulting layers became more stoichiometric as annealing temperature increased. The small part of Mo proved useful to prevent exaggerated grain coalescence. Reactive sputtering was more effective than inert deposition to achieve a nanograined layer with lowest size (31 nm). Mo segregated at the surface and partially sublimated as MoO3. The layers became n-doped semiconductors and were tested as chemoresistive gas sensors. Good capability to sense ethanol was determined within a range useful for applications. A model was proposed to explain the response to ethanol.