Structure-controlled Pt-based catalysts have been known to exhibit improved electrocatalytic activities due to particularly modulated surface structures favorable for hydrogen oxidation or oxygen reduction reactions. We prepare octahedral Pt-Pd alloy nanoparticles such as Pt₃Pd₁, Pt₁Pd₁, Pt₁Pd₃ by reducing metal ions with glycerol as a reducing agent in an aqueous solution. The octahedral Pt-Pd nanoparticles are well-defined alloy nanostructures with dominant {111} facets. Among them, the octahedral Pt₃Pd₁ shows excellent electrochemical properties i.e., much enhanced electrocatalytic activity and stability for oxygen reduction reactions in comparison with conventional Pt-based catalysts.