The demand for an efficient and clean fuel alternative has increased in recent years and is expected to become more pronounced in future, since many automotive companies have announced to potential appearance of commercially available fuel cell vehicles. Hydrogen is considered one of the best alternative fuels due its abundance, easy synthesis, and non-polluting nature when used in fuel cells. However, the main problems that have to be solved are the efficient storage and transport of this highly flammable gas. Extremely efficient hydrogen storage methods, from both the gravimetric and volumetric standpoints, are essential for automotive applications that mean a reversible hydrogen sorption capacity of 5-6 wt% at 100°C and 0.1 MPa. The main challenges in the field of hydrogen storage are to develop new materials or composites to exhibit 1) high volumetric/gravimetric capacity, 2) fast sorption kinetics at near-ambient temperatures, and 3) high tolerance to recycling. One of the most promising classes of materials for hydrogen storage are nanostructured composites, because they have different chemical, physical, thermodynamic and transport properties as compared to their bulk counterparts. In recent years there has been considerable interest in magnesium-based systems for hydrogen storage application. A number of studies have been carried out to improve the system, especially to enhance its sorption (absorption and desorption) kinetics. As it was already reported, milling or mechanical alloying is a common method to achieved nanostructures. It is well known that magnesium or other hydrogen storage alloys, if milled on their own, show a considerable improvement in sorption rate. But in order to enhance the kinetics, a variety of additives have been used. The positive effect is due, on the one hand, to the mechanical alloying which results in formation of a pure and reactive surface with dislocations and other defects and, on the other, to the presence of additives along with magnesium playing the role of catalysts in the hydriding and dehydriding processes. These additives may be 3d metals, 3d metal oxides, intermetallics such as LaNi5 (pure or partly substituted), MmNi5, YNi5, etc. A large number of investigations deal with materials of the Mg-Ni and Mg-Fe system. Recently the influence of graphite addition in presents of organic lubricants was studied. The present paper represents a study of the hydrogen absorption-desorption characteristics of magnesium composites in presence of transition metals Ni, Fe and Co. The composites was obtained by ball milling was performed under argon using stainless steel vial and balls in a Spex 8000 mixer/mill. X-ray diffraction (XRD) was obtained with a Rigaku DMAX-IIIC equipped with Cu-Ka radiation and graphite monochromator, while morphological characterization was carried out by SEM in a Cambridge 25GMK.III equipped with EDS. Hydrogen desorption measurements were performed by DSC 2010, TA Instruments. Several Mg-based hydrides were synthesized with different processing parameters in order to understand the structural stability of the nanocomposites hydrides, the role of the catalyst, of the microstructure and of the impurities on the sorption kinetics. The nanocomposite, in specific experimental conditions, combines some of the advantage of the high hydrogen capacity of magnesium with the lower temperature of operation of the other phase like Mg2Ni and in consequence can operate at temperatures as low as 220°C with fast kinetics and with total hydrogen capacity of above 5 wt.%.