In　order　to　assess　the　impact　of　different　carbon/nitrogen　(C/N)　on　anoxic/aerobic　sequencing　batch　reactor　(SBR)　nitrosation　system,　the　C/N　was　adjusted　to　0,　2/3,　1,　4/3,　2,　3,　6　at　room　temperature　(18-20).　The　results　showed　that　the　activated　sludge　system　with　the　influent　chemical　oxygen　demand　(COD)　loading　and　ammonia　loading　of　0.2　and　0.3　kg/(m3•d)　successfully　achieved　nitritation　only　after　24　d.　It　needed　more　time　to　achieve　nitritation　with　no　COD　in　influent.　When　the　C/N　was　less　than　6,　the　system　maintained　good　nitritation　performance　with　the　nitrosation　rate　of　over　90%.　When　the　C/N　was　6,　the　nitrosation　rate　dropped　to　70%.　When　the　C/N　was　4/3,　the　heterotrophic　bacteria　used　the　influent　COD　for　denitrification　adequately,　the　total　nitrogen　removal　efficiency　reached　49.8%,　and　the　COD　removal　efficiency　remained　above　80%.　Because　the　sludge　system　lacked　the　carbon　source,　the　total　nitrogen　removal　efficiency　increased　with　the　increase　of　the　C/N　when　it　was　less　than　4/3.　When　the　C/N　was　4/3　to　2,　the　COD　and　total　nitrogen　removal　efficiencies　almost　remained　unchanged.　When　the　C/N　was　2　to　6,　due　to　the　reduction　of　influent　ammonia　loading,　the　removal　efficiencies　of　COD　and　total　nitrogen　showed　a　downward　trend.　At　the　end　of　operation　(154　d),　COD　and　total　nitrogen　removal　efficiencies　were　64.8%　and　18%,　respectively.　When　the　C/N　increased　due　to　an　increase　in　COD,　the　proteins　(PN)　tended　to　increase　gradually,　and　polysaccharides　(PS)　almost　did　not　change,　while　the　decrease　in　ammonia　caused　an　increase　in　the　C/N,　PN　and　PS　decreased,　but　the　value　of　PN/PS　increased.　©　2019,　Editorial　Board　of　Journal　of　Harbin　Institute　of　Technology.　All　right　reserved.