The　filamentous　bulking　of　sludge　is　directly　associated　with　specific　influent　characteristics　and　operational　regime.　In　order　to　understand　whether　the　types　of　carbon　source　can　cause　filamentous　sludge　bulking　and　lead　to　the　formation　of　dominant　filamentous　bacteria,　their　long-term　effects　on　sludge　settleability　and　filaments　growth　as　well　as　the　competition　between　filaments　and　floc-formers　were　investigated.　Three　lab-scale　sequencing　batch　reactors　under　controlled　conditions　were　operated　by　using　acetate,　glucose　and　starch　as　carbon　sources,　respectively.　When　the　storage　capability　of　microorganisms　was　limited　by　decrease　of　substrate　concentration　gradient,　there　appears　a　great　quantity　reproduction　of　filamentous　bacteria　i.　e.　filamentous　bulking　(sludge　volume　index,　SVI＞600　ml·g-1)　for　acetate-　and　glucose-fed　systems.　SVI　was　kept　below　300　ml·g-1　for　starch-fed　reactor,　although　much　open,　fluffy　and　porous　flocs　were　formed,　and　settling　performance　had　no　serious　deterioration.　The　results　from　staining　reactions　and　fluorescent　in　situ　hybridization　showed　that　the　first　dominant　filament　was　Thiothrix　nivea　for　the　acetate-fed　reactor,　S.　natans　for　the　glucose-fed　reactor,　N.　limicola　II　and　M.　parvicella　for　the　starch-fed　reactor.　So,　it　was　demonstrated　that　various　carbon　sources　can　lead　to　different　metabolic　characteristics　for　various　substrates,　and　the　occurrence　of　filamentous　bulking　was　closely　associated　with　kinetics　and　storage　properties　of　microorganisms.　©　All　Rights　Reserved.