The nanoscaled Ni-based compounds (Ni3C, Ni3N, NiO and Ni2P) are synthesized by chemical methods. The MgH2-X (X = Ni3C, Ni3N, NiO and Ni2P) composites are prepared by mechanical ball-milling. The dehydrogenation properties of Mg-based composites are systematically studied using isothermal dehydrogenation apparatus, temperature programmed desorption system and differential scanning calorimetry. It is experimentally confirmed that the dehydrogenation performance of the Mg-based materials ranks as following: MgH2 Ni3C, MgH2 Ni3N, MgH2 NiO and MgH2 Ni2P. The onset dehydrogenation temperatures of MgH2 Ni3C, MgH2 Ni3N, MgH2 NiO and MgH2 Ni2P are 160 degrees C, 180 degrees C, 205 degrees C and 248 degrees C, respectively. The four Mg-based composites respectively release 6.2, 4.9, 4.1 and 3.5 wt% H-2 within 20 min at 300 degrees C. The activation energies of MgH2 Ni3C, MgH2 Ni3N, MgH2 NiO and MgH2 Ni2P are 97.8, 100.0, 119.7 and 132.5 kJ mol(-1), respectively. It' found that the MgH2 Ni3C composites exhibit the best hydrogen storage properties. Moreover, the catalytic mechanism of the Ni-based compounds is also discussed. It is found that Ni binding with low electron-negativity element is favorable for the dehydrogenation of the Mg-based composites. (C) 2017 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.