Pd@Pt core-shell nanocrystals consisting of well-defined Pd nanocube cores and dendritic Pt shells were prepared by a new facile aqueous one-pot synthetic method. The prepared Pd@Pt nanocrystals exhibited efficient catalytic activity and stability toward methanol electrooxidation, and their catalytic function was highly dependent on their Pt shell thickness due to the different synergism between Pt and Pd.