Aerobic granulation (AG) and membrane bioreactor (MBR) are two promising, novel environmental biotechnological processes that draw interest of researchers engaging work in the area of biological wastewater treatment. Membrane fouling in the combined, AGMBR process was investigated in this work. The fouling layer formed on hollow-fibre membranes in both reactors were for the first time directly observed with the multiple staining and confocal laser scanning microscope (CLSM) technique. Fouling layers in both reactors presented a rather heterogeneous fouling layer, with that on SMBR much more redundant than that on AGMBR. The EPS in the AGMBR fouling layer was principally consisted of proteins. alpha-polysaccharides, and lipids, with few beta-polysaccharides or cells. In SMBR, large quantity of DNA was probed in the fouling layer. Over-deposition of fouling layer on hollow-fibre membrane may assist preventing occurrence of irreversible fouling, which is beneficial to long-term operation of the AGMBR. (C) 2008 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.