Pt modified Pd/C catalysts were synthesized through galvanic replacement method in a one-pot synthetic process, where the replacement reaction was influenced greatly by the presence of the haloids (Cl- or Br-) in the solution. The catalysts with and without Pt modification were characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-Ray spectroscopy (EDX) and electrochemical tests. The modified state and atomic ratio of Pt to Pd due to the variation of synthetic conditions were confirmed by the physical characterizations. The variation in structure/surface composition of the Pt Pd/C catalysts leaded to different reaction mechanism and varied the performance of formic acid electrooxidation, which were confirmed by the electrochemical tests. The Pd/C catalyst modified with Pt in the presence of Cl- possesses satisfactory comprehensive performance, i.e. both stability and activity, for formic acid electrooxidation (FAEO). The results are of significance for designing catalysts for practical application of direct formic acid fuel cell and understanding mechanism of FAEO on noble metals composite structures. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.