Polyacrylonitrile (PAN) cationic and anionic exchange NF membranes were prepared from ultratiltration (UF) membranes through a convenient way developed recently by us. By the reaction between nitrite groups and NaOH or 3-(dimethylamino)propyl amine, negative or positive functional groups were introduced into the meso-macropores of PAN UF membranes. These meso-macropores were then reduced into the range of micromesopores by taking advantage of surface tension forces within the capillary pores during heat treatment in the presence of ZnCl2. The effective pore radius of the commercial cationic exchange NF membrane, NTR 7450, was measured from pure water permeability coefficients by a simple method, which utilized univalent alkaline ions as probes. (c) 2007 Elsevier B.V. All rights reserved.