Nanocrystalline (NC) materials, exhibiting a large surface area, may be used as gas sensors for which a large surface effect is required. 1n this study, NC TiO 2 was synthesized by means of the gas-evaporation method.The mean particle size of NC TiO 2 under 20 mbar of oxygen/helium (1: 4)was about 20 nm. The dopant, NC Pt less than 10 nm in diameter, was directly deposited onto the surface of NC TiO 2 to improve the sensitivity of NC TiO 2 -based sensor. The highest sensitivity was detected in NC 4.3 at% Pt/TiO 2 and is about 70 in 250 ppm H 2 S/Air at 500 o C and is higher than that of the pure NC TiO 2 which was 47 in the same sensing conditions. This temperature is lower than that of a traditional TiO 2 sensor (~700 o C) by about 200 o C. The response time of NC TiO 2 and NC Pt/TiO2 at 500 o C is less than 1 minute.