Hydrogenation and degradation properties of Mg-10wt% Ni hydrogen storage alloys were investigated by cyclic hydriding-dehydriding tests. Mg-10wt% Ni alloy was synthesized by rotation-cylinder method (RCM) under 0.3% HFC-134a/air atmosphere and their hydrogenation and degradation properties were evaluated by pressure-composition-isotherm (PCI) measurement. Hydrogen storage capacities gradually increased following 160 hydriding-dehydriding cycles and thereafter started to decrease. Measured maximum hydrogen capacity of Mg-10wt% Ni alloy is 6.97 wt% at 623 K. Hydriding and dehydriding plateau pressure were kept constant for whole cycles. Reversible hydrogen capacity started to descend after 280 hydriding-dehydriding cycles. The lamellar eutectic structure of Mg-Ni alloy consists of Mg-rich alpha-phase and beta-Mg2Ni. It is assumed that the lamellar eutectic structure enhances hydrogenation properties. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.