The　bacterial　diversity　of　an　aerobic　granular　sludge　in　municipal　wastewater　treatment　system　was　studied　by　the　construction　of　a　16S　rDNA　clone　library.　110　clones　were　randomly　selected　from　the　library.　The　corresponding　partial　16S　rDNA　gene　was　sequenced　and　blasted.　The　results　indicated　that　the　bacterial　community　in　GSBR　was　highly　diverse,　and　could　be　divided　into　fourteen　major　groups.　The　largest　fractions　were　Proteobacteria,　which　accounted　for　85.18%　of　the　total　clones.　The　dominance　order　was　β-Proteobacteria,　α-Proteobacteria,　γ-Proteobacteria,　uncultured　Bacteroidetes,　Candidate　division　TM7,　δ-proteobacterium,　Firmicutes,　Planctomycetacia,　Actinobacteria,　Sphingobacteria,　Flavobacteria,　Cytophagia,　Uncultured　bacterium,　and　Uncultured　anaerobic　bacterium.　Preliminary　analyzed　different　bacterial　population　in　nitrogen　and　phosphorus　removal　system,　among　them,　part　of　the　Proteobacteria　were　phosphorus　accumulating　bacteria.　Acidovorax　sp.,　Planctomycetacia,　Cytophagia,　and　Flavobacteria　had　nitrogen　removal　capacity.