This work presents results of the study of methanol electro-oxidation on gas diffusion electrodes with Pt-Ru catalysts supported on carbon. The catalysts were prepared by reduction with formic acid and their performance compared with Pt/C and Pt50Ru50/C E-TEK commercial catalysts, in half cell and single DMFC experiments. The results show that: (i) the activity of the catalysts in a half-cell depends on the concentration of methanol, the maximum being observed close to 2 mol l(-1); (ii) atomic contents of Ru of 25% and above increase the tolerance of the catalyst to larger methanol concentrations; (iii) the catalyst Pt75Ru25/C is the one that exhibits the larger activity for methanol oxidation. Gas diffusion electrodes built with this catalyst showed potentials 0.14 V higher than with Pt/C E-TEK when tested in single DMFC.