To examine the organic fouling mechanism of anion-exchange membranes (AEMs) based on electrostatic interaction, affinity interaction and geometrical factors, the time-voltage curves in an electrodialysis (ED) desalination process consisting of commercially available AEM and NaCl solutions containing organic substances with different chemical structures as organic foulants were measured. Aromatic organic substances cause more severe organic fouling on AEMs with chloromethylstyrene and divinylbenzene base matrix than aliphatic organic substances due to affinity interaction between the aromatic substances and the membrane matrix. AEMs with thin charged layers on membrane surfaces having the same charge as the charged groups of organic substances show higher anti-fouling properties than AEMs without charged layers due to electrostatic repulsion between the organic anions and the fixed charged groups of the thin charged layers. The AEM with an aromatic polymer matrix and with low water content is fouled more severely by the aromatic substances with a high molecular weight. (C) 2012 Elsevier B.V. All rights reserved.