The　effluent　of　an　Anaerobic/Oxic　(A/O)　process　removing　phosphorus　from　municipal　wastewater　was　used　as　influent　to　a　partial　nitrification　process.　Under　the　conditions　of　normal　temperature　(20~29°C)　and　limited　oxygen　(DO<0.2　mg·L-1),　the　mechanism　of　nitrification　and　the　factors　allowing　partial　nitrification　to　be　maintained　in　a　continuous　flow　process　while　treating　municipal　wastewater　were　investigated.　A　new　operation　mode　of　partial　nitrification　was　also　developed.　The　experimental　results　show　that　the　characteristics　of　the　inoculated　sludge,　sludge　concentration　and　aerobic/anoxic　alternating　operation　were　the　key　factors　influencing　maintenance　of　partial　nitrification　of　municipal　wastewater.　As　the　sludge　return　ratio　increased,　the　nitrite　accumulation　rate　increased　accordingly,　with　a　nitrite　accumulation　rate　of　85%　and　the　highest　value　of　96%.　Good　sludge　settlement　properties　were　maintained　with　SVI　values　of　70~110　mL·g-1　under　low　DO　conditions.　Average　effluent　NO2--N/NH4+-N　of　the　partial　nitrification　process　was　about　1.0,　which　could　produce　suitable　influent　for　the　anaerobic　ammonium　oxidation　(ANAMMOX)　reactor.　During　the　latter　period　of　the　experiment,　total　nitrogen　(TN)　removal　efficiency　was　about　50%　in　the　aerobic　reactor,　and　the　batch　experiments　verified　that　ANAMMOX　had　taken　place　in　the　reactor.　The　above　results　can　provide　helpful　background　for　developing　autotrophic　nitrogen　removal　from　municipal　wastewater　in　a　single　reactor.