Samples　were　collected　from　a　sequencing　batch　reactor　(SBR)　to　characterize　the　similarities　and　differences　in　microbial　community　composition　in　samples　using　Illumina　high-throughput　sequencing.　The　main　objective　of　this　study　was　to　characterize　changes　in　microbial　community　composition　during　filamentous　sludge　bulking　and　control　processes.　The　SBR　working　volume　was　11　L,　and　the　reactors　were　operated　for　399　days　in　total.　High-throughput　sequencing　results　indicated　that　rich　diversity　existed　in　the　microbial　communities　of　the　seeding　sludge.　Generally,　during　sludge　bulking,　microbial　composition　decreased,　and　after　the　sludge　was　remediated,　the　diversity　gradually　increased.　The　dominant　bacteria　in　the　seeding　sludge　were　Saprospiraceae_norank,　Comamonadaceae_unclassified,　and　Tetrasphaera,　comprising　13.37%,　10.54%,　and　8.59%　of　the　community,　respectively.　After　culturing　using　sodium　acetate　as　the　sole　carbon　source,　Thiothrix　and　Trichosporon　increased　significantly　from　the　seeding　to　the　bulking　sludge,　with　ranges　from　0.1%　to　60.14%　and　from　19.60%　to　94.82%,　respectively.　After　the　sludge　bulking　was　controlled,　the　relative　abundances　of　Thiothrix　and　Trichosporon　were　0.1%　and　2.32%,　respectively.　Therefore,　we　postulate　that　increases　in　filamentous　Thiothrix　and　Trichosporon　were　the　main　cause　for　the　sludge　bulking.　©　2018,　Science　Press.　All　right　reserved.