Mg-20wt% Ni-Y composite was successfully prepared by reactive mechanical alloying (RMA). X-ray diffraction (XRD) measurement showed that both MgH2 and Mg2NiH4 co-exist in the milled composite. The composite exhibits excellent hydrogen sorption kinetics and does not need activation on the first hydrogen storage process. It can absorb 3.92 and 5.59 wt% hydrogen under 3.0 MPa. hydrogen pressure at 293 and 473 K in 10 min, respectively, and desorb 4.67wt% hydrogen at 523 K in 30min under 0.02MPa hydrogen pressure. The equilibrium desorption pressure of the composite are 0. 142, 0.051 and 0.025 MPa at 573, 543 and 523 K, respectively. The differential scanning calorimetry (DSC) measurement showed that dehydrogenation of Mg-20wt% Ni-Y composite was depressed about 100K comparing to that of milled pure MgH2. It is deduced that both the catalysis effect of Mg2Ni and YH3 distributed in Mg substrate and the crystal defects formed by RMA are the main reason for improving hydrogen sorption kinetics of the Mg-20 wt% Ni-Y composite. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.