Hydrophilic modification of porous polyethersulfone (PES) membranes was achieved by Ar-plasma treatment followed by graft copolymerization with acrylamide (AAm) in the vapor phase. Both surfaces of the modified membranes were found to be highly hydrophilic, the permanency of which depends on the grafting yield. The graft reaction was confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The grafting rate was dependent on plasma exposure time. The surface and pore structures of PES membranes were viewed using scanning electron microscopy (SEM), revealing no surface damage and only a slight alteration in pore structure. As a result of the incorporation of polar functionalities, the glass transition temperature (T-g) of both the Ar-plasma treated and AAm grafted membranes increased. A moderate change in the tensile strength of the modified membranes was also observed. Most importantly, the AAm grafting made the membrane surface less susceptible to adsorption of BSA proteins. The grafted membranes also give greater flux recoveries after cleaning, indicating that the protein fouling layer was reversible because of the hydrophilic nature of the modified membranes.