Adsorption isotherms of hydrogen on activated carbon and multiwalled carbon nanotubes (MWNT) were collected using volumetric method for the range of 233-298 K and pressures up to 11 Mpa. The same shape of isotherms revealed a common mechanism of adsorption. However, the amount of H-2 adsorbed on MWNT is 3-5 times less than on activated carbon, but the surface concentration of H-2 on MWNT is 4-6 times higher than on activated carbon. Temperature exerts much less effect on the adsorption of H-2 on MWNT than on the adsorption of H-2 on activated carbon. Isosteric heat of adsorption was evaluated from a set of isotherms basing on the Clausius-Clapeyron equation, and -1.7 kJ/mol was obtained for MWNT, -6.4 kJ/mol was obtained for activated carbon. Considering the much less quantity adsorbed, the much less heat of adsorption and the much smaller surface area, carbon nanotubes seem not to be a promising carrier of hydrogen for practical applications. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.