The changes in surface stress of a gold film electrode during underpotential deposition (UPD) of lead in pH 3.0, 0.5 M NaClO4 solution containing 10(-4) M Pb(ClO4)(2) or PbCl2 were measured by a bending beam method to investigate the relation between surface stress and structural change of the Pb-UPD layer. A maximum in the surface stress vs. potential curve like an electrocapillary curve emerged at the onset of the UPD. Moreover, a hump in the surface stress vs. potential curve also emerged in the range of surface coverage of Pb from theta(Pb) = 0.4 to 0.8 during the UPD process. The changes in surface stress were plotted vs. cathodic charge required for Pb-UPD. Two linear and one plateau region appeared in the surface stress vs. the cathodic charge curve. The plateau region corresponded to the hump in the surface stress vs. potential curve. It was deduced from the comparison with the scanning tunnel microscopy, atomic force microscopy, and surface X-ray scattering spectroscopy results in the literature that the plateau region is associated with the change in rotation angle from R = 0degrees to 2.5degrees of incommensurate hexagonal close-packed Pb layer. Particularly, it was emphasized that the hump resulted from the release of compressive surface stress due to the change in rotation angle of the UPD layer. (C) 2004 The Electrochemical Society.