Abstract: The Pt/graphene (Pt/G) nanocomposite was prepared via a facile and clean one-step chemical reduction method. The obtained catalysts were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), which directly show that Pt nanoparticles (NPs) successfully assembled on grapheme and well distributed on the grapheme sheets. The further electrocatalytic characterization of the catalysts for methanol oxidation reaction (MOR) including cyclic voltammetry (CV) and chronoamperometry (CA) indicated that Pt/graphene has significantly higher electrocatalytic activity and stability for MOR compared to Pt. Chronocoulometry was used by controlling step potential to determine the diffusion coefficient of methanol in sulfuric acid which was 1.37×10^-9 cm²·s^-1 at 298 K, as well as the forward rate constants (k_f) at different potentials.