A single-walled, capped and selenium doped, carbon nanotube, Se@C-120, was doped endohedrally with hydrogen molecules to obtain a series of (nH(2) + Se) @CI120, (n: 0-11) systems. Then, they were subjected to quantum chemical treatment using PM3 method at the level of RHF approach. Calculations indicated that these systems were stable but endothermic in nature. In (10H(2) + Se@C-120) and (11H(2) + Se@C-120) systems, the hydrogen molecule nearest to the Se atom tends to dissociate to form a quasi-H2Se structure. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.