The relationship between extracellular polymerase substances (EPS) and sludge characteristic were investigated by extraction and analysis of EPS in different size biomass and membrane fouling in an aerobic granule membrane bioreactor (GMBR). The results indicated that the contents of EPS, polysaccharides and proteins in large granules (particle diameter, d > 0.45 mm) were significantly lower than that in small granules (d < 0.45 mm) and flocculent sludge. In addition, the content of EPS in membrane fouling was more than that in suspended biomass. For flocculent sludge, the sedimentation and filtering performance decreased markedly as increasing EPS content. However, for granular sludge, there was no significant correlation between EPS content and sludge characteristics. Furthermore, application of aerobic granule can improve sludge filtering properties and delay the process of membrane fouling, as a result of better morphological structure and lower EPS content. (c) 2010 Elsevier Ltd. All rights reserved.