Hydrogen desorption mechanism of a Mg-V composite prepared by spark plasma sintering (SPS) has been studied in this paper based on the thermodynamic and kinetic analysis. The results showed that the hydrogen desorption temperature of Mg in the Mg-V composite decreased by 109 K compared with that of pure Mg. By means of the pressure-composition-temperature (PCT) tests and the Van't Hoff equation calculation the enthalpy of MgH2 in the Mg-V composite was determined to be -82.7 kJ/molH(2), which was almost the same with that of pure Mg. Utilizing the non-isothermal kinetic mechanism function fitting the kinetic activation energy of hydrogen desorption in the Mg-V composite was determined to be 64.7 kJ/molH(2), which was 91.7 kJ/molH(2) lower than that of pure Mg. Thus, it can be concluded that the decrease of hydrogen desorption temperature of Mg in the Mg-V composite is mainly due to the improvement of hydrogen desorption kinetics. The thermal instability of MgH2 contributes little to the decrease of hydrogen desorption temperature. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.