A composite nanofiltration (NF) membrane was prepared by coating aqueous solution of chitin xanthate onto polyacrylonitrile UF membrane and subsequently cross-linked with H2O2 in ethanol. The effects of the membrane preparation conditions and operating conditions on performance of the composite membranes were studied. The results suggested that composite NF membrane with excellent rejection performance should be prepared with 1.0 wt.% of chitin xanthate concentration, 0.9 wt.% H2O2 concentration, 3.0 h cross-linking at 30 degrees C, and then 15 min heat treatment at 50 degrees C. The pressure osmotic coefficient of membrane was -4.2 mV MPa-1. Characterization results suggested: molecular weight cut-off of the resulting membrane was 652 Da; the rejections of the resulting membrane to Na3PO4, K2SO4, Na2SO4, MgSO4, KCl, NaCl and MgCl2 solutions (1000 mg L-1) were 91.85%, 90.65%, 85.65%, 53.39%, 40.29%, 40.53% and 28.44%, respectively, and the permeations were 11.73 L h(-1) m(-2), 13.75 L h(-1) m(-2), 13.91 Lh(-1) m(-2), 14.27 Lh(-1) m(-2), 14.18 Lh(-1) m(-2), 14.81 Lh(-1) m(-2) and 15.05 Lh(-1) m(-2), respectively, at the operating pressure of 0.40 MPa and cycling flow of 40 Lh(-1). Similar to other negative charged membranes, the rejection performance of the composite membrane depended on the electrostatic strength between the charged membrane and ions of electrolyte. With its high rejection to PO43- and SO42- ion, the membrane can be applied to the removal of PO43- and SO42- ion and the purification of water. (c) 2007 Elsevier B.V. All rights reserved.