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 0.20 eV/H 2 according to the approximation of GGA and 0.5 eV/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.