Self-supported 3D Mo doped WP2 nanowire arrays on carbon fiber paper (Mo-WP2 NWs/CFP) is prepared as an efficient monolithic electrode for electrocatalytic hydrogen evolution reaction (HER). The results indicate that the electrocatalytic performance can be significantly improved via doping. The sample with the Mo: W mole ratio of 5% only needs overpotential of 96 mV to afford the current density of 10 mA cm−2 with a small Tafel slop of 48 mV dec−1, which displays the best HER catalytic activity ever reported among the tungsten phosphides. The Mo doping enhances the electronic conductivity, increases the electrochemical active surface area and modifies the binding energies of P in the WP2, which notably improves its HER activities and develops it as a promising catalyst for energy storage and conversion.