The surface characterization of a Pt+Pd alloy electrode using copper deposited at underpotentials is described. The alloy was prepared by codeposition under the same conditions at all times. The surface of the Pt+Pd alloy (20at.% Pd) electrode was pretreated by simple flame annealing. The behaviour of the underpotentially deposited copper was studied as a function of time, deposition potential and CuSO4 concentration. The true surface areas, calculated from surface estimations based on the oxygen and copper monolayers, are compared.