Sodium　acetate　has　been　most　commonly　used　as　the　external　carbon　source　to　achieve　successful　performance　of　full-scale　enhanced　biological　phosphorus　removal　(EBPR)　processes,　but　its　microbial　mechanism　for　the　improvement　of　phosphorus　removal　performance　was　still　unclear.　DNA　based　stable-isotope　probing　(DNA-SIP)　is　able　to　discriminate　the　metabolic　activity　of　different　microbes　for　specific　substrates,　thus　it　was　applied　to　explore　the　different　effects　of　sodium　acetate　on　the　community　structure　of　Candidatus　Accumulibacter　(hereafter　called　Accumulibacter)　and　Candidatus　Competibacter　(hereafter　called　Competibacter)　in　a　modified　University　of　Cape　Town　(MUCT)　process　treating　the　real　domestic　sewage.　Results　showed　that　acetate　addition　significantly　improved　the　abundance　of　Accumulibacter　and　Competibacter　in　MUCT.　Accumulibacter　Glade　IID　exhibited　the　highest　proportion　in　all　clades　before　and　after　acetate　supplementation　but　the　proportion　decreased　from　95.4　%　on　day　23-66.3%　on　day　95.　Contrarily,　the　proportion　of　Glade　IIF　increased　from　0.9%　to　24%.　DNA-SIP　incubation　found　that　the　ratio　of　Accumulibacter　in　the　heavy　fractions　to　the　total　quantities　increased　faster　than　that　of　Competthacter,　which　successfully　revealed　the　acetate　assimilating　precedence　of　Accumulibacter　over　Competibacter.　Besides,　the　ratios　of　Accumulibacter　Glade　IIF　in　heavy　fraction　increased　by　22.3　%,　exhibited　a　higher　metabolic　activity　than　other　clades.　Adequate　acetate　accomplied　with　high　temperature　possibly　promoted　the　preferential　proliferation　of　Glade　IIF,　which　provided　a　way　to　enrich　Glade　IIF.　This　is　the　first　study　that　successfully　applied　DNA-SIP　to　discriminate　the　acetate　metabolic　activity　of　Accumulibacter　and　Competibacter,　and　Accumulibacter　clades.