Magnesium hydride (MgH2) is an attractive candidate for solid-state hydrogen storage applications. To improve the kinetics and thermodynamic properties of MgH2 during dehydrogenation-rehydrogenation cycles, a nanostructured MgH2-0.1TiH(2) material system prepared by ultrahigh-energy-high-pressure mechanical milling was investigated. High-resolution transmission electron microscope (TEM) and scanning TEM analysis showed that the grain size of the milled MgH2-0.1TiH(2) powder is approximately 5-10 nm with uniform distributions of TiH2 among MgH2 Particles. Pressure-composition-temperature (PCT) analysis demonstrated that both the nanosize and the addition of TiH2 contributed to the significant improvement of the kinetics of dehydrogenation and hydrogenation compared to commercial MgH2. More importantly, PCT cycle analysis demonstrated that the MgH2-0.1 TiH2 material system showed excellent cycle stability. The results also showed that the Delta H value for the dehydrogenation of nanostructured MgH2-0.1TiH(2) is significantly lower than that of commercial MgH2. However, the AS value of the reaction was also lower, which results in minimum net effects of the nanosize and the addition of TiH2 on the equilibrium pressure of dehydrogenation reaction of MgH2.