Mesoporous metals have attracted a lot of interest due to their wide range of applications, particularly in catalysis. We previously reported the preparation of mesoporous Pd using block copolymer micelle templates (Chem. Sci. 2019, 10, 4054). Here we extend this synthetic concept to generate alloyed spherical palladium-copper (PdCu) nanoparticles with an open porous network and uniform morphology. This one-pot synthesis is initiated by water-induced micellization of the block copolymer, followed by the chemical reduction, nucleation, and growth of mesoporous spherical alloy nanoparticles. Porosity enables accessibility to numerous active sites throughout the interior and exterior surfaces of the nanoparticles. Mesoporous nanoparticles composed of Pd and Cu alloy exhibit enhanced electrocatalytic activity and stability in the ethanol oxidation reaction (EOR) and the oxygen reduction reaction (ORR).