Hydrophilic nanofiltration membranes were prepared by grafting hydrophilic copolymers onto surface of ultrafiltration membranes. The method consists of a UV irradiation followed by an in situ graft co-polymerization of water soluble monomers on the membranes made of cardo polyetherketone (PEK-C). The effect of irradiation time and monomer nature on the membrane performance was investigated. Analysis by Fourier transform infrared in attenuated total reflection mode, contact angles and scanning electron microscopy of the membrane surface showed that the grafting degree and their hydrophilicity increase with irradiation time. The co-polymerization of hydrophilic monomers yielded better nanofiltration membranes, i.e. with higher permeation flux. The water flux through a membrane grafted for 10 min at a 5.2 mW cm(-2) UV-irradiation power changed from 1.46 L m(-2) h(-1) for poly(acrylic acid) to 9.69 L m(-2) h(-1) poly(acrylic acid-co-sodium allyl sulfonate) under a driving pressure of 0.2 MPa, for the sodium sulfate retention of 75%. (C) 2007 Elsevier B.V. All rights reserved.