MgH2, MgH2-TiH2 nanocomposites and their deuterated analogues have been obtained by reactive ball milling and their kinetic and cycling hydrogenation properties have been analysed by isotope measurements and high-pressure differential scanning calorimetry (HP-DSC). Kinetics of material synthesis depends on both Ti-content and the isotopic nature of the gas. For pure Mg, the synthesis is controlled by isotope diffusion in Mg and therefore MgH2 forms faster than MgD2. For the MgH2-TiH2 nanocomposites, the synthesis is controlled by the efficiency of milling. Kinetics of reversible hydrogen/deuterium sorption in nanocomposites have been studied at 548 K. The rate limiting step is isotope diffusion for absorption and Mg/MgH2 interface displacement for desorption. HP-DSC measurements demonstrate that the TiH2 phase acts as a gateway for hydrogen sorption even in presence of MgO and provides abundant nucleation sites for Mg and MgH2 phases. The 0.7MgH(2)-0.3TiH(2) nanocomposite exhibits steady hydrogen storage capacity after 100 cycles of absorption desorption. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.