Abstract: The electrocatalysts of platinum based PbSb surface alloy were prepared by electrochemical codeposition under cyclic voltammetric conditions. The structure and properties of these electrocatalysts were studied by techniques of cyclic voltammetry, electrochemical quartz crystal microbalance(EQCM), scanning tunneling microscopy(STM) and Xray photoelectron spectroscopy(XPS). The results demonstrated that the hydrogen evolution on the prepared electrocatalyst was postponed to －0.45 V. i.e., 200 mV has been shifted negatively in comparison with hydrogen evolution at a platinum electrode. In addition,the oxidization of Pb and Sb components in surface alloy was positively shifted to above 0.15 V, which is much higher than the oxidization potential of Pb and Sb metal electrodes. The stability of surface alloy electrode is confirmed to be higher than Pb and Sb metal electrodes that were employed often in organic electrosynthesis. The process of formation of surface alloy was studied in situ by using an EQCM and ex situ by using a STM. The results have converged to illustrate that the surface alloy is constructed of nanoparticles with regular size of about 10 nanometers.The EQCM analysis and XPS depth profiling indicated that the surface alloy is formed on the top layer of a few nanometers in thickness of the SbPbPt/GC electrode.