In　order　to　study　the　characterization　of　polyphosphate-accumulating　organisms　(PAOs)　community　structure　in　an　enhanced　biological　phosphorus　removal　system,　the　phosphorus　uptake　of　anaerobic-oxic　(A/O)　sludge　and　anaerobic-anoxic　(A/A)　sludge　were　investigated　via　batch　tests.　The　experiment　results　indicated　that　the　A/O　sludge　had　a　higher　aerobic　phosphorus　uptake　rate　than　the　anoxic　phosphorus　uptake　rate,　however,　the　aerobic　phosphorus　uptake　rate　of　the　A/A　sludge　was　less　than　the　anoxic　phosphorus　uptake　rate　of　that　sludge.　Based　on　these　results,　the　presently　used　method,　in　which　the　ratio　of　the　anoxic　phosphorus　uptake　rate　(qPa)　to　the　aerobic　uptake　rate　(qPo)　gives　the　relative　proportion　of　denitrifying　polyphosphate-accumulating　organisms　(DPAOs)　in　the　PAOs,　is　unreasonable.　Furthermore,　the　PAOs　community　structure　was　related　to　the　electron　acceptor　type.　According　to　the　type　of　electron　acceptor,　three　groups　of　the　PAOs　could　be　proposed　as　follows:　PON　(using　oxygen　and　nitrate　as　electron),　PO　(using　only　oxygen　as　electron　acceptor)　and　PN　(using　only　nitrate　as　electron　acceptor).