The　effect　of　the　different　P/C　ratios,　i.e.,　2.9/100,　1.4/100,　0.57/100,　0.29/100,　1.4/100　and　2.9/100,　on　the　dynamic　changes　of　the　phosphorus　removal　as　well　as　the　organism　community　was　examined　in　an　anaerobic/aerobic　sequencing　batch　reactor　(A/O-SBR)　system,　affiliated　with　Polymerase　Chain　Reaction-denaturing　Gradient　Gel　Electrophoresis　(PCR-DGGE).　Results　showed　that　when　the　P/C　ratio　dropped　(2.9/100→1.4/100→0.57/100→0.29/100)　gradually,　the　P-release　to　substrate-uptake　ratios　decreased　companied　by　an　increase　in　the　intracellular　glycogen　content.　Also,　the　DGGE　profiles　showed　that　with　the　decrease　of　the　influent　P/C　ratios　the　dominant　microbial　species　increased　from　11　operation　taxonomy　units　(OTUs)　to　14　OTUs,　and　then　dropped　to　7　OTUs.　Judged　from　the　biochemical　characteristics　of　the　SBR,　it　can　be　confirmed　that　the　predominant　microbial　populations　in　the　SBR　had　changed　from　PAOs　to　PAOs　and　GAOs　co-exist,　and　finally　to　GAOs.　For　the　last　recovery　period,　the　P-release　to　substrate-uptake　ratios　increased　gradually　with　the　decrease　of　the　intracellular　glycogen　content,　indicating　that　PAOs　can　be　re-cultivated　through　regulating　the　influent　P/C　ratio,　once　GAOs　had　dominated　the　EBPR　system.　While,　the　DGGE　profiles　showed　that　the　dominant　species　of　PAOs　re-cultivated　from　the　GAOs-dominated　system　was　different　greatly　from　both　the　GAOs-dominated　system　and　the　initial　PAOs-dominated　system.