The　effect　of　DO　(Dissolved　oxygen)　on　the　kinetics　of　nitrite　denitrification,　as　well　as　the　corresponding　N2O　accumulation　and　emission　were　investigated　using　2.4　L　sequencing　batch　reactor.　The　results　show　that　NaNO2　is　added　at　the　initial　of　the　test　to　the　final　NO2--N　mass　concentration　of　40　mg/L.　The　aeration　rate　is　controlled　at　0.3　L/min　and　the　ratio　of　N2　to　O2　is　adjusted　so　that　the　DO　can　be　controlled　at　0,　0.1,　0.3,　0.5　and　0.7　mg/L　and　the　N2O　emission　is　0.41,　0.60,　2.62,　4.98,　6.83　mg/L,　respectively.　The　denitrification　rate　decreases　with　the　increase　of　DO　mass　concentration.　The　nitrite　reduction　rate　per　gram　of　mixed　liquor　suspended　solid　(MLSS)　decreases　from　14.9　to　10.2　mg/(L　·　h),　while　the　N2O　emission　rate　per　gram　of　MLSS　increases　from　0.2　to　1.9　mg/　(L　·　h).　The　reason　may　be　that　higher　DO　mass　concentration　inhibits　the　activity　of　N2O　reductase　thus　results　in　higher　N2O　production　as　to　higher　N2O　emission.　Besides,　higher　nitrite　presence　inhibits　the　activity　of　nitrous　oxide　reduction　enzymes　which　is　responsible　for　N2O　reduction.　To　reduce　DO　mass　concentration　in　anoxic　tanks　during　nitrogen　removal　process　may　be　the　efficient　way　to　reduce　N2O　emission　during　nitrite　denitrification　process.