Abstract: Using potential sweep and potential time sequence techniques, we have studied the promotion of UPDof lead for the clcctrocatalytic oxidation of formic acid on platinum in HClO₄ aqueous solution. The results showed that the first oxidation peak in anodic direction and oxidation peak in cathodic direction in the cyclic vol-tammogram are due to the oxidation of the same intermediate which is adsorbed weekly and the second and the third anodic peaks in anodic direction are due to the oxidation of the two different intermediates which are adsorbed strongly. Furthermore, all these intermediates are the linear adsorption on platinum surface and they are probably single bonded species, HCOO_ab,, and multiple bonded species, CO_ab and COH_ab, respectively. Thus, the function of UPDof lead for the oxidation of formic acid is neither the third-body effect nor the decrease of hydrogen adsorption thus preventing the formation of poisoning species.The role of UPDof lead should be an electronic effect, that is, it acts by modifying adsorption property of platinum in such a way that the oxidation of intermediate HCOO_ab becomes easier.