Abstract: The ZnO nanoparticles,prepared from zinc nitrate and ammonia by deposition method,are analysed through the X-ray diffraction and TEM.The results show that the particles are global,very small（about 20 nm in size） and assigned to the hexagonal zincite-structure.The gas sensitive properties to chlorine gas are improved greatly by doping In₂O₃.The experiments show that the sensitivity of the component to 20×10^-6（volume percentage）chlorine gas is up to 301,the response time is 2 seconds,and the recovery time is about 110 seconds with high selectivity.