A newly proposed impedancemetric water-vapor sensor using yttria-stabilized zirconia (YSZ) and In2O3 sensing-electrode (SE) was found to be effective in the detection of various combustible hydrogen-containing gases, such as H-2 and hydrocarbons, at 900 degrees C under dry condition. This sensor can also detect the hydrogen-containing gases without interference of other gases such as CO, CO2, NO and NO2. Based on the results of gas chromatography, it is speculated that the hydrogen-containing gases are completely oxidized to H2O and CO, due to the high catalytic activity of In2O3 for the gas-phase oxidation reaction at high temperature, and then the produced H2O can be detected by the present water-vapor sensor. (c) 2005 Elsevier B.V. All rights reserved.