Carbon-supported Pt-Ni catalyst samples were prepared by the colloidal method and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopic (XPS) and transmission electron microscopy (TEM). Potentiodynamic was used to measure the performance of the electro-catalysts for the oxygen electro-reduction. The results indicate that the Pt-Ni alloy particles are distributed homogeneously on the carbon surface, and their particle sizes are 3-5nm. In the same alkali concentration solution, the activity and methanol-tolerance of Pt nano-particle catalysts are greatly enhanced by doping Ni. For the catalyst, the optimum atom ratio of Pt to Ni is Pt50Ni50/C, and its methanol-tolerance is enhanced markedly as compared with Pt/C. The maximal current of the oxygen electro-reduction over Pt50Ni50/C reaches 106 mA/mg, and the onset over potential is 50 mV less than that over Pt/C in 0.1mol/L KOH solution.