By theoretical analysis, we have explored the feasibility of functionalizing boron fullerene (B 80 ) by adsorbing Mg atoms for the application as hydrogen storage nanomaterials. Our results show that due to the charge transfer from Mg to B atoms Mg atoms reside above the pentagonal faces of the B 80 cage. The electric field induced around the positive charged Mg atoms polarizes H 2 molecules, and the resulting binding is strong enough to adsorb H 2 without dissociation. Further calculations indicated that the 12Mg-decorated-B 80 has a high hydrogen storage capacity storing up to 96 H 2 molecules with an ideal binding energy of 0.20eV/H 2 according to the approximation of GGA and 0.5eV/H 2 according to LDA, corresponding to a hydrogen uptake of 14.2%. This suggested a possible method of engineering new structure for high-capacity hydrogen storage materials with the reversible adsorption and desorption of hydrogen molecules.