In electrodialysis processes, membranes tend to loose some transport properties after a certain period of utilization. Two ion-exchange membranes, namely a homogeneous anion-exchange membrane (MX) and a heterogeneous cation-exchange membrane (MK-40), were used to investigate the ageing phenomenon and to highlight the characteristic parameters of these membranes which evolve most quickly with ageing. An artificial ageing was carried out under oxidizing conditions (i.e. peracetic acid, and P3 Active Oxonia (R) solutions) on both membranes. It was found that an increase in conductivity and swelling rate, implying a modification of the polymer chain structure with time, but without a significant deterioration of the functional groups since the exchange capacity remained almost constant. (c) 2009 Elsevier B.V. All rights reserved.