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　In　2O　3.　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.