Atomic hydrogen storage by carbon nanotubes (CNTs) at atmospheric pressure is studied using Pd and La catalysts for dissociation of H-2 into atomic hydrogen and formation of defects on CNT surfaces, respectively. The defect sites on CNTs as adsorption sites of atomic hydrogen are prepared by oxidation pretreatment using a La catalyst. Pd catalysts are then deposited on CNT surfaces for dissociation of H-2 into atomic hydrogen, which then spills over to the defect sites. In the best case, 1.0 wt % hydrogen is stored in the defective CNT with Pd particles at 1 atm and 573 K. The hydrogen desorption in temperature programmed desorption (TPD) experiments started at 700-900 K, which agreed with the annealing temperatures of CNTs prior to hydrogen storage. Also, the amount of hydrogen stored in CNTs decreased with increasing annealing temperature. These results are ascribed to the crystallization of the defective structure of CNT into graphitic structure. The activation energies of 46.6, 87.3, and 129.8 kJ/mol derived from the desorption peaks of hydrogen in the defective CNT with Pd particles vary from 46.6 to 129.8 0/mol, depending on the annealing temperatures at 523, 623, and 773 K, respectively. The difference in the activation energies is probably due to the energies required for the recrystallization of the defect sites into the graphite structure.