A novel sulfonated poly(vinyl alcohol) hydrogel was prepared by the sulfonation of a semicarbonized poly(vinyl alcohol) hydrogel with concentrated sulfuric acid, and its swelling properties, mechanical properties, and electroresponsive behavior in Na2SO4 solutions were studied. The results indicated that the hydrogel had a sandwich-type structure, and this was confirmed by scanning electron microscopy. The water take-up ability of the hydrogel decreased with the ionic strength of the Na2SO4 solution increasing. Young's modulus, the elongation at break, and the tensile strength of the hydrogel swollen in deionized water were 1.36 MPa, 165%, and 2.93 MPa, respectively. The hydrogel swollen in an Na2SO4 solution bent toward the cathode under noncontact direct-current electric fields, and its bending speed and equilibrium strain increased with the applied voltage increasing. There was a critical ionic strength of 0.03 at which the maximum equilibrium strain of the hydrogel occurred. With cyclical changes in the direction of the applied potential, the hydrogel exhibited good reversible bending behavior. On this basis, an artificial fish was designed. Under a cyclically varying electric field (the period was 2 s, and the voltage ranged from -15 to 15 V), the swimming speed of the artificial fish could reach 9.6 cm/min in an Na2SO4 solution with an ionic strength of 0.03. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2346-2353, 2010