A cation-exchange membrane based on a styrene/hydroxyethyl acrylate/lauryl methacrylate (Sty/HEA/LMA) terpolymer was prepared via a postsulfonation reaction for various sulfonation times. Sulfonic groups were introduced into the membrane structure with sulfuric acid as the sulfonating agent and silver sulfate as an initiator in a nitrogen atmosphere. Sulfonated Sty/HEA/LMA terpolymer membranes were characterized by Fourier transform infrared (FTIR) spectrometry and nuclear magnetic resonance as well as by determining the degree of sulfonation (DS), ion-exchange capacity (IEC), water uptake (WU), and electrical property of the membranes. The presence of sulfonic groups in the sulfonated Sty/HEA/LMA terpolymer was confirmed by FTIR, and the resulting membrane showed an IEC of 1.29 meq/g and an electrical resistance of 0.1 Omega cm(2). The WU of the prepared membranes increased with the DS at the reaction time. The surface morphology obtained by atomic force microscopy clearly showed an increase of roughness with reaction time. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 3180-3188, 2011