In our previous works, modified acrylic fiber samples with highly ion-exchange ability were described. These fibers contain Suitable functional groups such as amidoxime, amid, and amine groups in their molecular chains. In this work, swelling in fiber diameter and hydrophilic properties of the modified acrylic fiber samples, as important parameters affecting on ion-exchange efficiency, were investigated. The results showed that all modification treatments gave rise to diameter swelling ratio, but this does not mean that sample with highest swelling ratio in all cases can result in highest ability to ion-exchange. In other words, the relation between them was complicated, and several factors such as the kind and the size of ion adsorbent and crosslinking ability of chemical reagent were used for modification interfere in ion-exchange phenomena. The results of moisture adsorption indicate that incorporating functional groups by modification treatments enhance moisture adsorption in which samples with higher ion-exchange ability possess higher hydrophilic property. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 3843-3847, 2008