We studied the oxygen reduction reaction (ORR) on bare and Pt monolayer-covered single crystal Pd2Co(111) surfaces in 0.1 M HClO4 solution. A reversible hydrogen adsorption/desorption between 0.05 V and 0.40 V with the charge density of 210 µC cm-2 is observed on the Pd2Co(111) surface, which is not seen with Pd bulk crystals. The annealed Pd2Co(111) surface shows very stable i-E curves after numbers of cycles between 0.04 V and 0.97 V at rooms temperature. The Pt monolayer was placed on the annealed Pd2Co(111) surface by galvanic replacement of the Cu upd adlayer. The order of the surface activity for the ORR at room temperature in 0.1 M HClO4 solution is PtML/ Pd2Co(111) > Pt(111) > Pd2Co(111).