The　stability　of　partial　nitrification　at　different　dissolved　oxygen　(DO)　concentration　was　studied　in　SBR　at　room　temperature.　Under　the　low　DO　concentration　of　0.5mg/L,　the　partial　nitrification　kept　stable　for　75cycles　with　the　nitrite　accumulation　rate　(NAR)　higher　than　80%.　Until　105cycles,　the　NAR　gradually　decreased　and　the　partial　nitrification　transformed　to　the　complete　nitrification.　However,　using　the　same　sludge,　the　partial　nitrification　kept　long-term　stable　of　180cycles　under　the　DO　concentration　of　2.5mg/L.　Furthermore,　NAR　was　higher　than　90%.　These　results　indicated　under　high　DO　concentration,　the　stable　operation　of　partial　nitrification　can　be　maintained　for　a　long　period　of　time.　The　oxygen　half　saturation　constant　of　AOB　and　NOB,　and　qPCR　tests　indicated　that　low　DO　might　be　benefit　to　the　growth　of　Nitrospira　that　resulted　in　the　unstable　of　the　partial　nitrification.　Moreover,　under　high　DO　concentration,　AOB　had　higher　affinity　for　oxygen.　Therefore,　high　oxygen　concentration　could　maintain　long-term　stability　of　partial　nitrification.　©　2018,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.