Thermodynamics and kinetics of hydrogenation-dehydrogenation of nanometric iron (nFe) doped Mg-MgH2 system have been studied. The nFe-doped Mg could be hydrogenated even at 0 degrees C up to 45% of the theoretical hydrogen storage capacity within an hour. The dehydrogenation of nFe doped MgH2 starts below 150 degrees C. The remarkably improved hydrogenation-dehydrogenation kinetics could be attributed to the nano-engineered surface of MgH2 by nFe. The enthalpies of hydrogenation-dehydrogenation were found to be 76 kJ/mol, and 77 kJ/mol respectively. The activation energy of hydrogenation was evaluated as 41 +/- 2 kJ/mol which is same as the diffusion barrier of hydrogen in Mg matrix. The apparent activation energy of dehydrogenation of nFe-doped MgH2 was found to be 74 +/- 1 kJ/mol which is same as the enthalpy of dehydrogenation. The nFe-doped Mg-MgH2 system has shown cyclic stability up to 50 cycles without significant changes in the kinetics and hydrogen storage capacity. Three-dimensional diffusion seems to be controlling the dehydrogenation process.