in this work we report the sensing properties of undoped and ruthenium-doped tin oxide thin films (sno2, sno2:ru) with different thicknesses, in a controlled atmosphere of propane gas (c3h8) at different operation temperatures. the films were deposited onto soda-lime glass substrates by the spray pyrolysis technique at different deposition temperatures, namely, 300, 350, 400, and 450°c. all the films were annealed in vacuum at 400°c during 1 h in order to stabilize the surface physical characteristics. the sensing properties of the films were characterized by the surface electrical resistance ratio in a c3h8 atmosphere, and air as reference. maximum sensitivities, on the order of 1.4 and 7.4 were obtained for undoped sno2, and, sno2:ru thin films, respectively.