High activity and long-term stability are necessary for the electro-catalysts to be used in fuel cells. Herein, we report the facile fabrication of a yolk-shell Pd-Ni-P alloy based on the thermal ripening of aggregated nanoparticles. The material has abundant nanopores in both the core and the shell parts. Size distribution analysis based on density functional theory shows the width of the nanopores is around 15 nm. Based on the electrochemical active area of palladium, the supported yolk-shell Pd-Ni-P catalyst affords a high electro-catalytic activity (1.9 mA cm(-2) (Pd)) in methanol oxidation reaction which is 1.5, 3.1, 3.8, or 5.5 times higher than those of face-centered cubic Pd-Ni-P, amorphous Pd-Ni-P, Pd-Ni, or Pd nanoparticles, respectively. Impressively, 87% of the current density remains after 2000 cycles' cyclic voltammetry with yolk-shell catalyst as the anode, which is much superior to those values with other related Pd-based nanoparticles.