A solution-phase synthesis method was studied to prepare carbon supported Pt-Co alloy catalysts. The organic precursors of Pt acetylacetonate and Co acetylacetonate were reduced in a high boiling point solvent of octyl ether in the presence of oleic acid (OAc) and oleylamine (OAm) to produce fine Pt-Co nanoparticles, which were subsequently deposited on carbon support to obtain Pt-Co/C catalysts. Thermogravimetric analysis suggests that the stabilizers (OAc and OAm) can be removed by copious ethanol washing and subsequent moderate temperature heat-treatment (250 degrees C, under Argon atmosphere). X-ray diffraction patterns indicate that the average particle size is around 2.3 nm, and the lattice parameter is 3.868 angstrom for the heat-treated Pt-Co/C (40 wt%). Transmission electron microscopy images show very small Pt-Co alloy nanoparticles homogeneously dispersed on the carbon support with a particle size distribution of 2-4 nm for all Pt-Co/C samples. The elements composition of Pt and Co in the final Pt-Co/C catalyst can be well controlled, as evidenced by inductively coupled plasma atomic emission spectroscopy and energy dispersive spectroscopy analyses. Proton exchange membrane fuel cell tests show the heat-treated Pt-Co/C cathode catalyst has higher mass activity of oxygen reduction reaction than Pt/C at an operation voltage of 0.9V. this can be attributed to its smaller particle size and reduced lattice parameter. (C) 2009 Elsevier B.V. Ail rights reserved.