Two　same　lab-scale　sequencing　batch　reactors　were　developed　to　investigate　the　effect　of　organic　carbon　on　microbial　characteristics　in　partial　nitrification　system.　Partial　nitrification　is　effectively　achieved　through　aeration　time　and　dissolved　oxygen　control.　Results　indicated　that　the　addition　of　organic　carbon　inhibited　the　nitrification　reaction,　thus　increasing　the　total　nitrification　time.　However,　as　organic　matter　was　consumed,　it　did　not　inhibit　the　achievement　of　partial　nitrification.　Scanning　electron　microscope　pictures　showed　that　the　morphology　of　biomass　was　affected　by　organic　carbon,　which　made　spherical,　small　rod-shaped,　and　filamentous　cells　both　observed　and　distributed　all　over.　16SrDNA　cloning　results　showed　that　organic　carbon　had　little　effect　on　competitive　growth　of　phyla　alpha-Proteobacteria,　delta-Proteobacteria,　and　Bacteroidetes;　was　beneficial　to　that　of　phyla　gamma-Proteobacteria　and　Planctomycetes;　went　against　that　of　phyla　Acidobacteria,　Nitrospira,　Spirochaetes,　and　Chloroflexi.　Bacterial　species　comprised　by　phylum　beta-Proteobacteria　could　be　easily　influenced　by　organic　carbon.　In　addition,　organic　carbon　affected　the　species　related　to　nitrogen　removal,　especially　that　are　not　good　for　competitive　growth　of　ammonia-oxidizing　bacteria.　Interestingly,　the　major　function　of　Denitratisoma　oestradiolicum　may　be　affected　by　organic　carbon.　In　addition,　species　of　ammonia-oxidizing　bacteria　were　affected　by　organic　carbon,　which　was　positive　for　Nitrosomonas　europaea,　but　Nitrosomonas　sp.　was　also　the　dominant　one.