Deformation of ionic polymer gel films in electrolyte solutions was studied under the influence of electric fields. The ionic polymer gel films used were poly(vinyl alcohol)-poly(sodium acrylate) composite gel films with a thickness of the order of submillimetres. The vibration of gel films in a.c. electric fields, has been observed for the first time. It was suggested that the vibration behaviour was based on a differential swelling. The vibration of the ionic gel films was roughly analysed as a mechanical bending of a uniform cantilever beam by sinusoidally varying forces.