Chloroxylenol　(PCMX),　an　antibacterial　agent,　has　been　widely　detected　in　water　environment　and　has　toxic　effects　on　biology　and　ecology.　During　270　d,　the　influence　of　PCMX　on　the　performance　of　three　nitrification　systems　was　investigated,　including　floc-based　sequencing　batch　reactor　(FSBR),　aerobic　granule-based　SBR　(AGSBR)　and　biofilm　SBR　(BSBR).　The　nitrification　capability　of　three　systems　was　inhibited　by　PCMX,　but　recovered　after　domestication,　and　PCMX　made　three　systems　realize　partial　nitrification　for　10,　100　and　35　days,　respectively.　The　extracellular　polymeric　substances　of　three　systems　increased　first　and　then　decreased　with　the　increment　of　PCMX.　The　granular　structure　of　AGSBR　may　be　conducive　to　the　enrichment　of　antibiotic　resistance　genes　(ARGs),　and　almost　all　ARGs　of　BSBR　were　reduced　during　the　addition　of　5.0　mg/L　PCMX.　The　microbial　community　results　showed　that　Rhodococcus　as　potential　degrading　bacteria　was　continuously　enriched　in　three　systems.　Piscinibacter　was　regarded　as　the　potential　antibiotic　resistant　bacteria,　which　was　positively　associated　with　multiple　ARGs　in　three　systems.　Additionally,　quaternary　ammonium　compounds　resistance