Acetaldehyde gas-sensing properties of SnO2, loaded with and without a noble metal, were investigated, and the results are discussed in terms of the level of sensor resistance in air and oxidation behavior of acetaldehyde over sensor materials. Of the noble metals tested, Rh was found to be the best sensitizer, and the highest sensitivity was achieved with SnO2 loaded with 0.1 wt % Rh at 350 degrees C. The sensitivity enhancement is explained by the increased sensor resistance in air due to the electronic interaction between Rh and SnO2. In addition, the almost complete oxidation of acetaldehyde and its derivatives at 359 degrees C is also found to be responsible for its high sensitivity.