Anion-exchange membranes with a semi-interpenetrating network structure were prepared by blending poly(vinyl alcohol) and a polycation, poly(allyl amine), in varying ratios. The membranes obtained were physically cross-linked by annealing them at various temperatures and/or chemically cross-linked by reaction with glutaraldehyde aqueous solutions. The water content of the membranes can be controlled easily by changing the annealing temperature and the concentration of the cross-linker. The charge density increases during the initial stage, and then decreases with increasing polycation content after reaching a maximum value. The membrane resistance is proportional to a function of water content, which means that the value of the resistance will be estimated from the water content. The membranes in this study are easily prepared and have high mechanical strength. Hence, the membranes will have potential application to the desalination of salt water at low salt concentration.