Novel bimetallic PdxCoy alloy nanoparticle (NP)/carbon nanofiber (CNF) composites with superior electrocatalytic performances were successfully prepared by electrospinning Pd and Co precursors, i.e., Pd(acac)2 and Co(acac)(2), in polyacrylonitrile followed by a thermal treatment. Uniform dispersion of PdxCoy nanoparticles in carbon nanofibers was achieved. Chemical composition and size of the resulting PdxCoy NPs, which showed a substantial effect on the electrocatalytic properties of PdxCoy/CNF nanocomposites, can be readily controlled by adjusting the feed ratio of metal precursors. In comparison with commercial Pd/C and other state-of-the-art Pd- or Pt-based catalysts, PdxCoy/CNF nanocomposites prepared in this study exhibited much higher electrocatalytic activity and stability in formic acid and methanol oxidation reactions. This improved electrocatalytic performance is very attractive for fuel cell applications and can be attributed to the unique bimetallic Pd Co alloy formation, a modified electronic structure of Pd in PdxCoy, as well as uniform dispersion and firm embedment of PdxCoy NPs in CNF.