Chemical treatment is a facile method for improving electrochemical properties of a heterogeneous ion-exchange membrane. In this work, polyvinylchloride (PVC)-based heterogeneous cation-exchange membrane is prepared by a dry-wet phase inversion process. The membrane is treated with a sulfuric acid solution in a room and a high temperature (80 degrees C). Effects of the treatment procedure and hydrophilic additive on membrane electrochemical properties are investigated. Chemically treated PVC and PVC/additive heterogeneous cation-exchange membranes show a change in membrane electrochemical properties in terms of water uptake (Wu), conductivity, ion-exchange capacity (IEC), and permselectivity (Ps). In general, Wu and conductivity increase after the chemical treatment. Significant improvement is observed when a high temperature is used. Meanwhile, the conductivity is more pronounced for PVC/additive membranes. The improvement may be associated with an increase in hydrophilicity. A significant increase in IEC is also observed for modified PVC/additive membrane. This may be associated with the removal or leaching of the additive during the treatment which in turn increases the portion of ion-exchange resins in the membrane. Most of the modified membranes show a decrease in Ps. It may be due to a decrease in the effectiveness of Donnan effect indicated by Donnan equilibrium constant (K+). POLYM. ENG. SCI., 59:E219-E226, 2019. (c) 2018 Society of Plastics Engineers