In2O3 gas sensing material was synthesized by a one step electrochemical-deposition process with 3.0 V working voltage and 40 A/m(2) current density using indium salt as a raw material. The crystal structure and morphology of In2O3 nanocrystals were characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectrometer. The results indicated that the structure of In2O3 without being treated was cubic structure In2O3 nanocrystals with mean grain size of 20 nm, and roundness morphology. Gas sensitivities of In2O3-based gas sensors to different kinds of gases were tested by mixing gas in air at steady state. The results indicated that the sensors showed fast response to 50 ppm H2S in air, the gas response is 149 times, response time is 2 s, and the relationship between response and H2S concentration is correlated linearly in a log-log scale. (c) 2006 The Electrochemical Society.