In2O3 nanoparticles were prepared from or with different indium salts by chemical precipitation under the conditions of various pH values. The crystal structure and ceramic microstructure of the samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the mean grain size of In2O3 is less than 100 nm, and their particle homogeneity and dispersibility are satisfactory. The gas sensitivity defined as Ra/Rg was detected in a static system. The results show that the sensors made by as-prepared nanoparticles has high sensitivity to many gases such as alcohol, HCHO, NH3, et al. The response time is less than 20 s and the recovery time is lower than 30 s.