We demonstrate a facile hydrothermal one-pot synthesis method for producing single crystalline mesoporous PtPd bimetallic nanoparticles with a hollow interior and porous surface structure in the presence of Br^- and I^- ions. The formation process analysis indicated that the coexistence of Br^- and I^- ions is responsible for the formation of the novel bimetallic nanoparticles. The changes in the reduction potential of Pt and Pd metal ions achieved by the coordination with different halide ions resulted in the formation of hollow interiors as a galvanic reaction between Pd²⁺ and Pt⁴⁺ ions occurred. In addition, the size of the mesoporous PtPd nanoparticles can be well controlled by slightly changing the amount of I^- ions used. The electrochemical tests indicated that the as- synthesized single crystalline mesoporous PtPd hollow nanoparticles exhibited enhanced catalytic properties toward methanol and ethanol oxidation reactions as compared with the commercial Pt black and Pt/C materials.