Cost-effective Mo2C nanocrystals homogeneously distributed in interconnected mesoporous carbon nanofibers are prepared through an electrospinning route combined with a subsequent pyrolysis process. The crystal phases of the Mo2C nanocrystals are controllable and their phase-dependent electrocatalytic activities for the hydrogen evolution reaction (HER) are explored. The nanocomposite catalyst made of the hexagonal-phase Mo2C nanocrystals in carbon nanofibers exhibits outstanding electrocatalytic kinetics and high activities for the HER in both acidic and basic media. It is found that the overpotentials are 160 mV in 0.5 M H2SO4 and 92 mV in 1 M KOH at a current density of 10 mA cm(-2). The Tafel slopes of 66 mV dec(-1) in 0.5 M H2SO4 and 63 mV dec(-1) in 1 M KOH are achieved. Also, the as-obtained Mo2C/C electrocatalyst shows long-term durability. (C) 2018 Elsevier Ltd. All rights reserved.