Well-dispersed Pt-Cu alloy nanoparticles (NPs) with a diameter of only approximate to 2 nm encapsulated in carbon nanofibers (CNFs) are synthesized using electrospinning technology followed by a graphitization process in a chemical vapor deposition furnace. Distinctly, even with a small amount of Pt, the Pt-Cu/CNFs-1:2 catalyst possesses outstanding hydrogen evolution reaction (HER) activity, including small overpotential, long-term stability, and a high exchange current density as well as large double layer capacitance (C-dl). The excellent HER performance of the Pt-Cu/CNFs-1:2 catalyst is attributed to the synergistic interaction between Pt and Cu, the uniform distribution of the alloy NPs and the use of CNFs with 3D architectures. This development may provide a simple, efficient, and green synthesis method to design bi- or multimetal alloys for use as the cathode electrocatalysts for the HER or other electrocatalytic devices.