We examined the hydrogen adsorption of palladium-embedded carbon nanotubes (CNTs) under ambient temperature and hydrogen partial pressures: 0.66-2.2 MPa. Nano-crystalline palladium is embedded in the MWCNTs via impregnation and in situ reduction reaction. The maximum reversible hydrogen storage exhibited by nanocomposite materials, measured at 298 K and 1.6 MPa is 0.18 wt% which is nearly twice the storage capacity of pristine CNTs. However, the storage capacity of the composite materials is approximately an order less than that of the palladium nanoparticles. The enhanced storage capacity is due to cumulative hydrogen adsorption by CNTs and Pd nanoparticles. We observe no significant difference between the reversible storage capacities of the composites made by two methods, which implies that the storage capacities of the samples essentially depend on the uptake by CNTs. (c) 2007 Elsevier B.V. All rights reserved.