Pt-Os (3:1)/C catalyst was prepared through the route of thermal decomposition of metallic carbonyl cluster. TEM image showed Pt-Os nanoparticles were well dispersed on carbon substrate with an average particle size of 2.2 +/- 0.9nm. XRD pattern indicated Pt-Os has a face-centered cubic crystal structure. Characterized by cyclic voltammetry and chronciamperometry. Pt-Os (3:1)/C catalyst shows a superior electro-catalytic activity to formic acid oxidation in comparison with Pt/C catalyst. This improved electrocatalytic performace was mainly due to the fine dispersion of Pt-Os nano particles and bi-functional effect. (C) 2008 Elsevier B.V. All rights reserved.