Poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) can be crosslinked by interfacial polymerization to develop a positively charged dense network structure. According to this mechanism, a positively charged hollow-fiber composite nanofiltration (NF) membrane was prepared by quaternization to achieve a crosslinked PDMAEMA gel layer on the outer surface of polysulfone hollow-fiber ultrafiltration (UF) membranes with a PDMAEMA aqueous solution as a coating solution and p-xylylene dichloride as an agent. The preparation conditions, including the PDMAEMA concentration, content of additive in the coating solution, catalyzer, alkali, crosslinking temperature, and hollow-fiber substrate membrane, were studied. Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize the structure of the membranes. This membrane had a rejection to inorganic salts in aqueous solution. The rejection of MgSO4 (2 g/L aqueous solution at 0.7 MPa and 25 degrees C) was above 98%, and the flux was about 19.5 L m-2 h-1. Moreover, the composite NF membranes showed good stability in the water-phase filtration process. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013