Effects of temperature seasonal change on sludge characteristics and membrane fouling in a pilot-scale submerged membrane bioreactor (MBR) were studied. Results showed that bound extracellular polymeric substances (EPS), soluble chemical oxygen demand (SCOD), polysaccharides, and proteins in the supernatants all increased under low temperature operation. The increase of diluted sludge volume index (DSVI) and capillary suction time (CST) indicated that the settling and dewatering ability of mixed liquors deteriorated. It was also found that the increase of EPS, polysaccharides, and proteins led to the increase of biopolymers attached to membrane surfaces and in turn caused severe membrane fouling.