The　characteristics　and　microbial　community　of　nitrifying　bacteria　cultivated　at　the　low　DO　concentration　of　0.3~0.5　m　g/L　in　a　sequencing　batch　reactor　(SBR)　was　investigated　in　this　study.　The　bacterial　abundance　and　diversity　were　analysed　with　different　influencing　factors　after　successful　cultivation　of　the　active　sludge.　Results　showed　that,　the　optimum　temperature　for　low-DO　nitrifying　bacteria　was　25,　and　the　optimum　pH　was　8.5.　Under　the　condition　of　pH　7.5　at　20,　specific　ammonia　oxidate　rate　and　specific　nitrite　oxidate　rate　were　0.3　and　0.6　mgN/(mg　MLSS·d)　with　DO　of　0.5~4　m　g/L,　respectively.　High　throughput　sequencing　analysis　revealed　that　Nitrospira　genus　was　the　dominant　nitrite　oxidizing　bacteria　(NOB)　accounting　for　33%　of　whole　community,　and　Nitrosomonas　was　the　major　ammonium　oxidizing　bacteria　(AOB)　accounting　for　7%　in　the　low-DO　nitrification　reactor.　©　2017,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.