Pt-Ru binary catalysts were prepared on a polyaniline-functionalized multiwalled carbon nanotube (PANi/MWCNT). PANi/MWCNT composites were synthesized by the polymerization of aniline in the presence of a carbon nanotube suspension using FeSO4 and (NH4)(2)S2O8 as the oxidants. The Pt-Ru/PANi/MWCNT catalysts were formed by the chemical reduction of H2PtCl6 and RuCl3 using NaBH4 as the reducing agent. The binary component catalyst is sharply distributed, with particle sizes ranging from 2.0 to 4.0 nm, and the Pt and Ru distributions are homogeneous when supported on PANi/MWCNT. In comparison, the binary catalyst supported on bare MWCNT displayed a Pt-rich core and a Ru-rich shell nanostructure. The surface composition deduced from CO stripping potentials confirms that the Ru surface content (chi(Ru)) is approximately 50% for the Pt-Ru alloy on PANi/MWCNT, and the catalyst on bare MWCNT shows nearly 70% Ru on the surface. Pt-Ru binary catalysts supported on PANi/MWCNT have higher activity, a higher Pt utilization efficiency, and much better durability when compared to other catalyst supports on bare MWCNT or on Vulcan XC-72.