Abstract: The catalytic property and gas sensitivity of indium oxide with different particle size and various dopants to ethanol were investigated systematically in micro-reactor,gas chromatography and gas sensing testing apparatus.The results showed that,by employing nano-indium oxide,the sensitivity to ethanol could be increased from 6.0 to 16.0.The sensitivity of indium oxide doped with basic metal oxide to ethanol was increased from 6.0 to 14.0.The sensitivity of indium oxide doped with noble metal to ethanol decrease because of its too large catalytic activity.Gas sensing performance was intrinsically depended on the catalytic property.Ethanol gas sensing mechanism of indium oxide was analyzed briefly.