Monodisperse nickel phosphide (Ni5P4) nanoparticles supported on carbon (Ni5P4@C) were in situ synthesized by one step solution-phase route, in which the mixture of trioctyloxide (TOPO) and trioctylphosphine (TOP) was used as solvent, capping agent and phosphor source. Ni5P4nanocrystals were in situ coupled by active carbon simply adding the carbon to the reaction solution. The as-prepared Pt-free Ni5P4 nanocrystals exhibit the enhanced electrocatalytic activity toward hydrogen oxidation reaction (HOR) compared to pure commercial Ni nanoparticles. Therefore, the obtained Ni5P4@C nanocatalyst appears to be promising non precious metal electrocatalysts for HOR.