Poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) can be crosslinked by quaternization to develop a positively charged dense network structure. According to this mechanism, PDMAEMA/polysulfone (PSF) positively charged nanofiltration membrane was developed by interfacial crosslinking polymerization using PSF plate microfiltration membrane as support layer, PDMAEMA aqueous solution as coating solution, and p-xylylene dichloride/n-heptane as crosslinking agent. Technique and condition of developing membrane such as concentration of coating solution, coating time, pH value of coating solution, content of low molecular weight additive in coating solution, concentration of crosslinking agent, crosslinking time, and number of coatings were studied. FTIR, SEM, and X-ray photoelectron spectroscopy were used to characterize the structure of membranes. This membrane had rejection to inorganic salts in water solution, the rejection rate to MgSO4 (1 g/L water solution at 0.8 MPa and 30degreesC) was about 90%, and permeation flux was about 10-20 L m(-2) h(-1). (C) 2003 Wiley Periodicals, Inc.