This article provides a novel method for introducing zwitterionic polymers into nanofiltration membranes, with the aim of achieving high water flux and good anti-fouling performance. Terpolymers P(DMC-HEA-DMAPS) (PDHD) composed of 2-methacryloyloxy ethyl trimethylammonium chloride (DMC), 2-hydroxyethyl acrylate (HEA) and 3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate (DMAPS) were synthesized via aqueous phase free-radical copolymerization. Composite nanofiltration membranes (CNFMs) were prepared with PDHD and glutaraldehyde (GA) via the combination of surface coating and chemical cross-linking methods. Chemical structures and compositions of PDHDs and CNFMs were characterized by (attenuated total reflectance) Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy and atomic force microscopy. The water permeability of CNFMs was examined with nanofiltration test and dynamic water contact angle measurement. Optimum nanofiltration performance was obtained for CNFM3 with 4.35 mol% DMAPS, e.g. R-MgCl2 = 96.5%, J(MgCl2) = 47.8 L m(-2) h(-1) (testing with 1 g L-1 aqueous MgCl2 solution at 25 degrees C and 0.6 MPa). Moreover, the extent of fouling for CNFM3 was significantly reduced and most of the fouling was reversible during the MgCl2 and protein filtration test. Therefore, the water permeability and anti-fouling property of CNFMs were significantly improved with introducing zwitterionic groups into the membranes. (C) 2011 Elsevier B.V. All rights reserved.