A novel composite nanofiltration (NF) membrane was prepared by over-coating the PAN ultrafiltration (UF) membrane with a glycolchitin (GC) thin layer. The effects of the membrane preparation techniques and operating conditions on the rejection performance of the composite membranes were studied. The structure of the composite NF membrane was characterized by scanning electron microscopy (SEM) and infrared spectroscopy (IR). And the surface roughness of the composite membrane was also characterized by atomic force microscope (AFM). The pressure osmobic coefficient (beta) was about -2 mV/MPa and the molecular weight cut-off (MWCO) was obtained at 540 Da or so. Rejections of the composite membrane of Na2SO4, K2SO4, MgSO4, NaCl, KCI, MgO2 solutions (1.0 g/L) were 95.2%, 91.5%,41%, 31.1%, 31 % and 20.1% at 25 degrees C under 1.0 MPa, and permeation fluxes are 10.0, 10.1, 19.2, 19.7, 20.8 and 13.0 L/m(2) h, respectively. The results suggest that rejection performance is governed by solute-membrane and solute-solute electrostatic interactions. This charge distribution mainly determined the performances of the membranes. (c) 2007 Elsevier B.V. All rights reserved.