A novel composite nanofiltration (NF) membranes were prepared using quaterinized chitosan as a selective layer, poly(acrylonitrile) OF membrane as a support layer and anhydride mixture as cross-linking reagent. The images of these membranes were characterized by scanning electron microscope, and the other characterizations such as pure water permeability, molecular weight cut-off, rejection and swelling were investigated. Molecular weight cut-offs tested were in the range of 550-580 Da (in NF range). Both pure water permeability and swelling in water decreased, whereas rejection increased with an increase in anhydride mixture concentration, indicating pore contraction and the increase in both hydrophobicity and pore tortuosity due to cross-linking. Besides, the rejection declined with the increasing feed concentration, whereas it was not affected by feed cross-flow rate. The order of rejection to different salts followed the decreasing of CaCl2, MgCl2, NaCl, KCI, MgSO4, Na2SO4 and K2SO4, suggesting the positively charged characteristic of the NF membranes. And the rejections to MgCl2, CaCl2 solutions reached up to 0.95, so the membranes developed can be used for the hardness removal in water treatment process. (c) 2007 Elsevier B.V. All rights reserved.