Novel ion-exchange membranes, which can control their hydrophilicity in response to temperature changes, are prepared by casting dimethyl sulfoxide solution of mixed poly (vinyl alcohol)(PVA), polyelectrolytes, and in situ polymer of PVA and N-isopropylacrylamide (NIPAAm). The water content of the membranes decreases with increasing temperature. This indicates that the hydrophilicity of the membrane matrix can be controlled by changing the temperature. The charge density of the membranes increases with temperature. The permselectivity through the membranes, which is defined as the division of permeation coefficient of NO₃^- ion to that of F- ion, increases at 50°C, but decreases at 15°C with increasing poly (NIPAAm) content. This indicates that the permselectivity between the ions through the membranes can be controlled by changing the temperature and the poly (NIPAAm) content.