The effect of the mechanical activation medium on the hydrogen absorption-desorption properties of MgH2 with NiCo2O4 additives is investigated. The composite 90 wt.% MgH2-10 wt.% NiCo2O4 mechanically activated for 180 min under hydrogen reaches a higher absorption capacity as compared to the composite ground for the same time in an argon medium. At T = 573 K and P = 1 MPa the composite activated mechanically in a reactive medium shows a value of 5.67 wt.% while for the composite ground under argon the value is 4.36 wt.% only, both samples preserving a high absorption capacity at temperatures below 573 K. Addition of nickel cobaltite is found to have a favorable effect on the hydriding kinetics of magnesium. In order to elucidate this effect, a composite containing a large amount of NiCo2O4 (50 wt.%) is also investigated. (C) 2009 Elsevier Ltd. All rights reserved.