In situ synthesis of Pd nanoparticles supported on multiwalled CNT (carbon nanotubes) is reported. The size of the nanoparticles can be easily tuned via application of different experimental conditions. The hydrogen storage properties of Pd supported on CNT at room temperature were examined in the pressure range of 0-50 bar. Carbon material with palladium particles of 3 nm diameter exhibits the highest hydrogen capacity at low moderate pressure than the raw materials and CNT with larger particles size of 17 and 9 nm, respectively. We also propose the mechanism of hydrogen storage in the studied samples. (C) 2014 Elsevier Ltd. All rights reserved.