Using　glucose　as　cosubstrate,　activated　sludge　that　could　effectively　biodegrade　40　mg/L　2-chlorophenol　was　successfully　domesticated　in　sequencing　batch　reactors.　To　acclimate　the　sludge,　2-chlorophenol　was　increased　stepwise　from　0　to　40　mg/L.　High-throughput　sequencing　revealed　that　the　microbial　community　richness　increased　during　the　first　S　d　of　acclimation　to　5　mg/L　2-chlorophenol　and　then　decreased　after　another　20　d　as　2-chlorophenol　was　increased.　The　original　sludge　obtained　from　a　water　resource　recovery　facility　had　the　highest　microbial　diversity.　As　the　acclimation　continued　further,　community　richness　and　diversity　both　increased,　but　they　decreased　again,　significantly,　when　2-chlorophenol　reached　40　mg/L.　Saccharibacteria_norank,　Bacillus,　Saprospiraceae_uncultured,　and　Lactococcus　were　the　dominant　bacteria.　Bacillus　and　Pseudomonas　were　the　main　known　chlorophenol-degrading　bacteria.　WCHB1-60_norank,　Tetrasphaera,　Comamonadaceae_unclassified,　and　Haliangium　showed　poor　tolerance　to　2-chlorophenol.　Higher　bacterial　tolerance　to　chlorophenols　does　not　mean　higher　degrading　capability.　The　degradation　of　chlorophenols　was　not　positively　correlated　with　the　detected　abundance　of　known　2-chlorophenol-degrading　bacteria.