Hydrogen adsorption of multi-walled carbon nanotubes (MWNTs) was investigated under moderate pressure (12 MPa) at room temperature. The effects of annealing and doping on the hydrogen adsorption of carbon nanotubes have been discussed. It is showed that both heat-treatment and doping play an important role in the hydrogen adsorption of carbon nanotubes. Even when doped with the same element, the hydrogen uptake property was greatly different when the concentration of the doping solution changed. An optimal result (3.2 wt.%) was achieved for carbon nanotubes annealed in NZ at 500degreesC and soaked in 1.0 M KNO3 solution. (C) 2002 Elsevier Science B.V. All rights reserved.