Abstract: 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.