The nano-grained Pd or Pt-doped SnO₂ thin films were deposited on the alumina substrate at ambient temperature or 300 ℃ by using an R.F. magnetron sputtering system and then annealed at 650 ℃ for 1 hour or 4 hours in air. The crystallinity and microstructure of the annealed films were analyzed. A grain size of the thin films was 30 nm to 50 nm. As a result of gas sensitivity measurements to an alcohol vapor of 36 ℃, the 2 wt.% Pt-doped SnO₂ thin-film sensor deposited at 300 ℃ and annealed at 650 ℃ for 4 hours showed the highest sensitivity.