In order to increase hydrophilicity and thereby to reduce membrane fouling caused by hydrophobic adsorption, the surface of a hydrophobic 0.2 microm polypropylene (PP) membrane was modified by ozone treatment followed by graft polymerization with 2-hydroxy-ethyl methacrylate (HEMA). The modified PP (MPP) membranes were characterized in terms of contact angle, morphology and degree of grafting (DG). The contact angle was reduced from 112 degrees for a PP membrane to nearly 0 degrees for MPP membranes by introducing functional groups such as hydroxyl (-OH) and carbonyl groups (C=O) on the membrane surface. As the DG increased, the O/C ratio and membrane resistance of the MPP membrane increased. Using the MPP membrane in the crossflow operation of an anaerobic membrane bioreactor (MBR), the membrane permeability was enhanced although it was largely dependent on the DG of MPP.