A novel method of modification of cation exchange membrane for improved permiselectivity is reported in this paper. Acrylic acid grafted fluorinated ethylene propylene copolymer membrane after sulphonation (FEP-g-AA-SO3H) was used as the cation exchange membrane for modification. Polyaniline is deposited electrochemically on to the membrane. The deposition of polyaniline starts from the surface of the membrane and growth proceeds inside the membrane. The amount of polyaniline deposited depends upon the polymerization time. The presence of polyaniline is confirmed by FTIR, scanning electron microscopy, X-ray mapping, cyclic voltammetry and. ion exchange capacity measurements. The electrodialysis experiments show improved permselectivity for divalent cations. (c) 2007 Elsevier Ltd. All rights reserved.