Nanocrystalline MgH2/MexOy composite powders were produced by high energy ball milling (MexOy=Sc2O3, TiO2, V2O5, Cr2O3, Mn2O3, Fe3O4, CuO, Al2O3, SiO2). The hydrogen absorption and desorption kinetics were determined in view of a technical application. The addition of selected oxides lead to an enormous catalytic acceleration of hydrogen sorption compared to pure nanocrystalline hydrides. In absorption, the catalytic effect of TiO2, V2O5, Cr2O3, Mn2O3, Fe3O4, and CuO is comparable. Concerning desorption, the composite material containing Fe3O4 shows the fastest kinetics followed by V2O5, Mn2O3, Cr2O3 and TiO2. Only 0.2 mol% of the catalysts is sufficient to provide a fast sorption kinetics. Additionally, Mg absorbs hydrogen already at room temperature by the use of metal oxides as catalysts. Furthermore, it is demonstrated for the first time that MgH2/MexOy-powders release hydrogen at 200°C.