Composite membranes were prepared by chemical polymerization of a thin layer of polyaniline (PANI) in the presence of a high oxidant concentration on a single face of a sulfonated cation-exchange membrane (CEM) and quaternary aminated anion-exchange membrane (AEM). IR and SEM studies for both types of membranes confirmed PANI loading on the ion-exchange membranes. PANI composite ion-exchange membranes were characterized as a function of the polymerization time by ion-exchange capacity, coating density, and membrane conductance measurements. Membrane potential measurements were performed in various electrolyte solutions in order to observe the selectivity of these membranes for different types of counterions. Membrane potential data in conjunction with membrane conductance data was interpretated on the basis of frictional considerations between membrane matrix and solute. Electrodialysis experiments, using PANI composite ion-exchange membranes with 4 h polymerization time, were performed in single and mixed electrolyte solutions for observing electronmigration of solute across PANI composite ion-exchange membranes. Relative dialytic rates of Na2SO4, CaCl2, and CuCl2 were estimated with reference to NaCl on the basis of electrodialysis experiments and it was concluded that it is possible to separate different electrolytes using PANI composite ion-exchange membranes. (C) 2004 Elsevier Inc. All rights reserved.