In the present study, we have investigated the combined effect of different transition metals such as Ti, Fe and Ni on the de/rehydrogenation characteristics of nano MgH2. Mechanical milling of MgH2 with 5 wt% each of Ti, Fe and Ni for 24 h at 12 atm of H-2 pressure lead to the formation of nano MgH2-Ti5Fe5Ni5. The decomposition temperature of nano MgH2-Ti5Fe5Ni5 is lowered by 90 degrees C as compared to nano MgH2 alone. It is also found that the nano MgH2-Ti5Fe5Ni5 absorbs 5.3 wt% within 15 min at 270 degrees C and 12 atm hydrogen pressures. However, nano MgH2 reabsorbs only 4.2 wt% under identical condition. An interesting result of the present study is that mechanical milling of MgH2 separately with Fe and Ni besides refinement in particle size also leads to the formation of alloys Mg2NiH4 and Mg2FeH6 respectively. On the other hand, when MgH2 is mechanically milled together with Ti, Fe and Ni, the dominant result is the formation of nano particles of MgH2. Moreover the activation energy for dehydrogenation of nano MgH2 co-catalyzed with Ti, Fe and Ni is 45.67 kJ/mol which is 35.71 kJ/mol lower as compared to activation energy of nano MgH2 (81.34 kJ/mol). These results are one of the most significant in regard to improvement in de/rehydrogenation characteristics of known MgH2 catalyzed through transition metal elements. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.