Performance　of　sludge　settling　property　and　filamentous　bacteria　growth　under　nitrite　existing　conditions　were　studied.　Biomass　was　cultivated　in　three　anoxic/aerobic　sequencing　batch　reactors.　Two　of　them　were　dosed　with　nitrite　to　the　anoxic　and　aerobic　phases,　respectively,　leaving　the　remaining　one　without　nitrite　added　as　control.　The　results　showed　that　nitrite　had　a　significant　negative　effect　on　sludge　settling　property;　a　serious　bulking　[sludge　volume　index　(SVI)＞350mL/g]　and　a　limited　bulking　[SVI　about　220mL/g]　were　observed　in　the　anoxic-　and　aerobic-nitrite-dosed　systems,　respectively.　Filamentous　bulking　more　easily　happened　when　nitrite　existed　in　the　anoxic　conditions　than　in　the　aerobic　conditions.　There　were　almost　no　differences　in　terms　of　filamentous　species　between　the　nitrite-dosed　and　non-nitrite-dosed　systems,　which　indicated　that　nitrite　did　not　play　a　key　role　in　determining　the　filamentous　species.　The　nitrite　existing　under　both　anoxic　and　aerobic　conditions　showed　a　negative　effect　on　microbiological　intracellular　storage　capability.　The　maximum　polyhydroxyalkanoates　(PHAs)　production　and　the　maximum　specific　PHA　production　rate　in　nitrite-dosed　systems　were　both　significantly　lower　than　that　in　the　control　system.