The structure of the Au(lll) surface in contact with a recast Nafion(R) film has been studied as a function of potential by using grazing incident angle X-ray diffraction. The high penetration depth of X-ray makes it possible to probe the electrode surface covered by a 1 to 3 mu m thick Nafion(R) film. The Nafion(R)-coated Au(lll) electrode surface is not reconstructed at open circuit potential. However, the (23 x root 3) reconstruction can be generated at sufficiently negative potentials. In comparison with the Au(lll) electrode in NaClO4 solution, the lifting of reconstruction is shifted positively by about 0.2 V. This fact supports the view of the primary effect of surface charge on the Au(lll) reconstruction lifting. Adding chloride to the solution shifts the phase transition potential negatively after several hours, indicating a moderate ion permselectivity of the Nafion(R) film in NaCl solution. These results demonstrate that the Nafion(R) coating is stable over a large potential range and is suitable for studying surface properties and the effects of ion distribution on surface electrochemical processes at single crystal surfaces.