The effects of membrane preparation conditions on membrane properties were studied in detail. The results suggested that composite nanofiltration (NF) membrane from 2.0 wt % 2-hydroxypropyltrimethyl ammonium chloride chitosan (HACC) vaporized for 2.5 h at 50 degrees C, and then crosslinked for 9 h at 50 degrees C with hexamethylene diisocyanate (HDI)/ethanol (0.45/50 wt/wt) were found to have optimal performance. The resultant membrane was called HACC/PAN [poly(acrylonitrile)] NF membrane. The characteristics of this membrane such as pure water permeability, molecular weight cut-off, rejection of salts, and swelling were investigated. And its cut-off molecular weight (MWCO) was -520 Da. At 25 degrees C and 1.0 MPa, the permeability of water was 17.24 L/h m 2 MPa. Swelling in water decreased and rejection of salts increased with increasing HDI concentration, indicating pore contraction and increase in hydrophobicity as well as pore tortuosity due to crosslinking. The order of rejection to different salt solutes followed the decreasing of CaCl2, MgCl2, NaCl, KCl, and Na2SO4, suggesting that this membrane was positively charged. The rejections to MgCl2 and CaCl2 were more than 0.90; therefore, this membrane can be used for hardness removal in water treatment process. (c) 2007 Wiley Periodicals, Inc.