The　bacterial　diversity　in　an　anoxic/aerobic　membrane　bioreactor　process　(A/O-MBR)　was　studied　by　16S　rDNA　cloning　and　sequencing　method.　The　experimental　results　showed　that　the　clone　library　of　aerobic　sludge　sample　comprised　9　major　groups.　The　largest　fractions　were　Proteobacteria　and　Bacteroidetes,　which　accounted　for　37.04%　and　14.81%　of　the　total　clones,　respectively.　The　protions　of　Acidobacteria,　uncultured　bacterium,　Planctomycetes,　Chlorobi　and　uncultured　Chloroflexi　bacterium　were　11.11%,　11.11%,　5.56%,　7.41%　and　7.41%,　respectively.　The　relatively　lower　portions　were　1.85%　Nitrospirae　and　1.85%　Euglenozoa.　The　clone　library　of　anoxic　sludge　sample　was　found　to　include　10　major　groups,　the　largest　fractions　were　Proteobacteria,　Bacteroidetes　and　uncultured　bacterium,　which　accounted　for　27.91%,　13.95%　and　12.79%,　respectively.　The　protions　of　Planctomycetes,　Acidobacteria　and　Chloroflexi　in　this　library　were　9.3%,　9.3%　and　9.3%,　respectively.　The　relatively　lower　portions　were　6.98%　Nitrospirae,8.14%　Euglenozoa,1.16%　Gemmatimonadetes　and　1.16%　Actinobacteria.　The　main　bacteria　groups　were　similar　in　the　two　pools,　but　the　species　and　proportions　were　different.　Proteobacteria　was　identified　to　be　the　main　denitrifer　genera　in　the　system.　©,　2015,　Science　Press.　All　right　reserved.