The　performance　of　denitrifying　phosphorus　removal　under　nitrification　and　nitritation　was　investigated　in　a　lab-scale　Modified　University　of　Cape　Town　(MUCT)　process　treating　real　domestic　wastewater　with　low　C/N　ratio.　The　experimental　results　of　180　days　showed　that　nitritation　was　achieved　at　short　hydraulic　retention　time　(HRT)　and　low　dissolved　oxygen　(DO)　of　0.3-0.5　mg　x　L(-1),　and　an　average　nitrite　accumulation　rate　(NAR)　of　above　70%　was　achieved　during　nitritation　stage.　The　MUCT　process　showed　a　good　performance　of　denitrifying　phosphorus　removal.　Under　nitritation　mode,　total　and　denitrifying　phosphorus　removal　efficiencies　were　90%　and　91%,　respectively;　under　nitrification　mode,　total　and　denitrifying　phosphorus　removal　efficiencies　were　60%　and　88%,　respectively.　Although　phosphorus　removal　performance　under　nitritation　was　better　than　that　under　nitrification,　the　results　of　fluorescence　in　situ　hybridization　(FISH)　indicated　that　the　percentage　of　phosphorus　accumulating　organisms　(PAOs)　in　biomass　was　about　37%　under　two　modes.　The　effluent　COD　concentration　was　below　50　mg　x　L(-1)　during　the　experimental　period.　Batch　tests　of　different　nitrifying　sludges　showed　that　the　percentage　of　denitrifying　phosphorus　removal　bacteria　(DPBs)　in　PAOs　using　NO2(-)-N　as　an　electron　acceptor　under　nitritation　mode　was　almost　the　same　as　that　using　NO3(-)-N　as　an　electron　acceptor　under　nitrification　mode,　with　an　average　percentage　of　38%.　Compared　with　nitrification　mode　with　conventional　phosphorus　removal,　nitritation　mode　with　denitrifying　phosphorus　removal　has　a　superior　performance　treating　limited　carbon　source　wastewater.