Nanofiltration (NF) is considered to be an intermediate process between ultrafiltration (UF) and reverse osmosis (RO). In the present work, chitosan derivative containing carboxylic acid group (-COOH), i.e. N,O-carboxymethyl chitosal (NOCC), is prepared. Then, the NOCC composite NF membrane having a polyether sulfone (PES) UF membrane as the substrate is prepared using a method of coating and crosslinking, in which glutaraldehyde solution is used as the crosslinking agent. The developed membranes are characterized in terms of Fourier transform infrared/attenuated total reflectance (FTIR/ATR), scanning electron microscopy/energy dispersive V ray analysis (SEM/EDXA), elemental analysis (EA), swelling behavior, tensile strength, and thermogravimetric analysis (TGA), which confirm the formation of the target membranes. Rejection efficiency of nickel ions from aqueous Solutions, of nickel sulfate and nickel chloride, is investigated. The experiments are carried Out for different feed concentrations, feed flow rates and applied pressures and the corresponding permeate flux and rejections are measured. The maximum observed rejection is found to be 80 and 62% of 5 ppm, 78 and 59%, of 10 ppm; and 74 and 57% of 50 ppm feed concentration of nickel sulfate-water and nickel chloride-water systems, respectively. The observed order of the separation of the nickel salts is NiSO4 and NiCl2. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 3596-3605, 2008