In order to search high-capacity hydrogen storage media, first-principles calculations were performed. Ca-decorated on perfect and defective C3N nanotube as a new adsorbent for H-2 molecules were studied. It was found that the Ca-decorated on defective nanotube can adsorb up to eight H-2 molecules with the average binding energy of 0.11 eV/H-2. Interaction of Ca atom with the nanotubes and H-2 molecules are explained by Dewar coordination and Kubas interaction, respectively. Furthermore, the binding energy of the Ca atom on the defective nanotubes at least two times larger than the perfect one. Hence, clustering of the Ca atom on the nanotubes can be prevented by defect region. Copyright (C) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.