Polyaniline fiber (PANI) was synthesized by chemical interfacial method and doped with para toluene sulfonic acid (PTSA) through a sequential doping-dedoping-redoping process resulting in PANI-PTSA. The doped material was utilized to fabricate Vulcan-polyaniline composite of C-PANI-PTSA. Next, through reduction, Pt particles were deposited on to this composite to produce a Pt/C-PANI-PTSA electrocatalyst. To investigate the PANI-PTSA interaction with the carbon support as well as, to consider its effect upon the catalytic activity of Pt/C-PANI-PTSA, electrocatalysts with different ratios of 10, 15, 20, 25 and 30 wt% were synthesized and their activity was compared with the Pt/C (Electrochem). Results revealed that, the peak current density in methanol electro-oxidation, electrochemical surface area, methanol diffusion coefficient, charge transfer resistance as well as; the stability of the Pt/C-20%PANI-PTSA electrocatalyst were all markedly improved for the synthesized material. Moreover, the Pt/C-20%PANI-PTSA was demonstrated to be more CO tolerant according to the CO stripping voltammetry test. Also powder XRD and TEM techniques were utilized to investigate the crystallite size and the surface morphologies of the catalysts. Finally, the performance of Pt/C-20%PANI-PTSA was compared with Pt/C (Electrochem) in a passive direct methanol fuel cell and the effect of PANI-PTSA on methanol crossover and fuel utilization was analyzed. Ultimately, the Pt/C-20%PANI-PTSA modified catalyst was shown to be more suitable for applying in the direct methanol fuel cells (DMFC) compared with the commercial Pt/C material. (C) 2013 Published by Elsevier Ltd.