Polyaniline/carbon nanotube composites as Pt catalyst supports for methanol electro-oxidation have been reported. Conventionally, the size and distribution of Pt catalysts were improved in the presence of polyaniline (PAni), and an interaction between Pt and N atoms in PAni could prevent Pt catalysts from aggregation and detachment. In this work, polyaniline-modified multi-walled carbon nanotube (PAni-MWCNT) composites, with different loading levels of PAni, were synthesized by in situ oxidative polymerization of aniline on the surface of MWCNT. And Pt catalysts supported by these composites were prepared by the liquid phase reduction. Our studies revealed that the loading level of PAni affected the proportion of the different valence Pt components. And the proportion of Pt(0) and Pt(II) was also important for improving the electro-catalytic performance of Pt catalysts. The proper proportion of Pt(II) was essential for coordination of Pt with oxygen-containing ligands (OH center dot, H2O) and thus accelerating oxidation of Pt (CO)(ads) with release of CO2 by improving the tolerance to intermediate carbonaceous species.