Sorption equilibria of the dicarboxylic acids, oxalic, succinic, adipic, and malic acids, and the tricarboxylic acid, citric acid, by the strongly basic anion-exchange membrane (SELEMION AMV) were studied to obtain the fundamental data for the development of a model of electrodialysis process to separate those acids. These acids were increasingly sorbed with increasing pH and solution concentration, while the sorption of citric acid reached a maximum at pH about 4, and gradually decreases. Non-dimensional selectivities of ionic species of these acids by the membrane were determined by an ion-exchange model that considered the dissociation of carboxylic acid in the solution, and electro-neutrality in the solution and in the membrane. The selectivities of mono-, di-, and tricarboxylic acids were correlated with their molecular weight as well as those of eight mono carboxylic acids. These results are useful for the general estimation of selectivity of carboxylic acids. (C) 2003 Elsevier B.V. All rights reserved.