Batch　filtration　tests　were　carried　out　to　investigate　the　membrane　biofouling　characterizations　of　nitrifying　and　denitrifying　sludge　from　a　continuous-flow　nitrogen　and　phosphorus　removal　bench-scale　membrane　bioreactor　under　the　stable　operation.　Biofouling　mechanisms　of　denitrifying　sludge　by　using　different　electron　donors　were　also　analyzed　and　discussed.　The　test　results　show　that　the　denitrifying　rate　by　using　the　acetic　acid　as　the　electron　donor　is　13.8　mg/(g·h),　higher　than　methanol　3.4　mg/(g·h),　ethanol　10.2　mg/(g·h)　at　25°C;　compared　with　nitrifying　sludge,　the　protein　of　soluble　microbial　products　from　denitrifying　sludges　increases　in　the　range　of　100　kDa,　being　the　main　factor　for　the　increased　resistance　of　soluble　substances　in　the　mixed　liquor,　thereby　increasing　the　pore　blocking　resistance　of　soluble　substances,　and　denitrification　process　by　using　the　methanol　as　the　electron　donor　is　the　most　obvious.　It　is　also　found　that　the　decrease　of　extracellular　polymeric　substances　produced　through　denitrification　processes　and　relative　hydrophobicity　of　carbohydrate　and　protein　substances　becomes　the　main　factor　for　the　decreased　resistance　of　SS　fraction　in　the　mixed　liquor;　the　relative　molecular　mass　distributions　of　extracellular　polymeric　substances　becomes　slightly　different　after　denitrification,　but　Fourier　transform　infrared　spectroscopy　of　the　functional　groups　of　extracellular　polymeric　substances　shows　that　the　chemical　composition　of　extracellular　polymeric　substances　produced　by　nitrifying　sludge　and　denitrifying　sludge　by　using　three　different　electron　donors　have　not　changed.　The　modified　fouling　index　of　denitrifying　sludge　by　using　acetic　as　the　electron　donor　becomes　the　lowest　one.