Thin films of undoped and Ca-doped SnO 2 were deposited by ion beam sputtering (IBS). The films annealed at 650 o C possess good adhesion and only SnO 2 single-phase. The CH 4 sensitivities of a thin film sensor are mainly affected by surface roughness together with agglomeration of primary particles of SnO 2 . The highly dense, single-phase SnO 2 film sensors exhibit greatly excellent long-term stability. Differently from the sensing behaviors for a sintered or a thick film sensor, Ca addition to SnO 2 as a crystallite growth inhibitor causes lower sensitivity for the thin film sensor.