Nitrospira　and　Nitrobacter　are　two　dominant　types　of　nitrite-oxidizing　bacteria　(NOB).To　evaluate　the　effect　of　dissolved　oxygen　(DO)　on　microbial　community　of　NOB　under　the　intermittent-aeration　mode,　the　population　and　microbial　community　of　this　two　NOB　types　were　investigated　in　an　aeration　reactor　with　low　DO　period　(55d)　and　high　DO　period　(113d).　Results　showed　the　population　of　Nitrospira　was　much　higher　than　that　of　Nitrobacter　during　the　low　DO　period　(0.2~0.5mg/L),　and　most　clones　of　Nitrospira　was　very　similar　to　the　clone　Candidatus　Nitrospira　defluvii.　After　increasing　DO　to　a　high　level　(1.5~2.3mg/L)　and　operating　for　113d,　Nitrobacter　turned　to　the　dominant　group.　Most　clones　of　Nitrobacter　were　distributed　to　the　branch　containin　Nitrobacter　winogradskyi.　Furthermore,　the　nitrite　accumulation　occurred　in　this　reactor　during　the　shift　of　population　between　Nitrospira　and　Nitrobacter　after　increasing　DO,　and　it　gradually　disappeared　when　Nitrobacter　became　the　dominant　NOB　group.　©　2016,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.