The　impacts　of　the　carbon　source　(sodium　acetate,　ethanol)　and　C/N　ratio　(1.0,　3.0,　and　5.0)　on　nitrogen　removal　and　membrane　fouling　behavior　were　investigated　using　a　denitrifying　membrane　bioreactor　(DNMBR)　treating　nitrate-rich　wastewater.　The　results　showed　that　the　C/N　ratio　showed　a　more　significant　impact　on　the　process　performance　than　the　carbon　source.　The　nitrogen　removal　efficiency　(NRE)　was　slightly　higher　when　employing　sodium　acetate　as　the　electron　donor　at　different　C/N　ratios.　The　nitrogen　removal　improved　with　an　increase　in　the　C/N　ratio　due　to　the　increased　specific　degradation　rate　of　NO3--N　(SDRNO3--N);　the　NRE　increased　from　24.43%　and　13.23%　at　a　C/N　ratio　of　1.0%　to　97.79%　and　96.46%　at　a　C/N　ratio　of　5.0　for　the　sodium　acetate　and　ethanol　systems,　respectively.　The　fouling　rate　accelerated　due　to　decreased　particle　size　and　increased　metabolic　production,　which　resulted　in　the　deterioration　of　sludge　rheological　properties　and　dewaterability　with　an　increase　in　the　C/N　ratio.　The　membrane　fouling　rate　with　sodium　acetate　supporting　the　DNMBR　was　lower　than　that　of　the　ethanol　system　at　different　C/N　ratios,　which　was　attributed　to　different　fouling　mechanisms.　The　high　(＞100　kDa)　carbohydrate　molecular　weight　fraction　of　soluble　microbial　production　played　an　important　role　in　membrane　pore-blocking　in　the　sodium　acetate　system.　For　the　ethanol　system,　the　high　(＞100　kDa)　molecular　weight　protein　fraction　of　extracellular　polymeric　substances　and　smaller-sized　particles　formed　a　denser　cake　layer.　Fourier　transform　infrared　analysis　showed　the　carbohydrate-like　and　protein-like　substances　were　the　main　membrane　foulants　throughout　the　entire　operation.