In an effort to prepare new hydrogen storage materials, we successfully obtained three types of polymer-derived nanoporous SiCx (x = 5-7) fibers, whose specific surface areas (SSAs) are larger than 580 m(2)/g. Their hydrogen adsorption properties were studied with a comparison of multi-walled carbon nanotubes (MWCNTs). The results reveal that micropores play a predominant role in hydrogen adsorptions at 77 K and at pressures below 0.5 MPa, and mesopores begin to take greater effect when the pressure increases beyond 0.5 MPa. The maximum hydrogen storage capacity (HSC), 0.33 wt% at 302 K and 4 MPa, was achieved for SiCx-KN fibers with SSA of 990 m(2)/g, while the HSC of the MWCNTs is 0.09 wt% at the same conditions. For these new materials, this work demonstrates that small pore size, large micropore volume and large SSA are all beneficial for the high hydrogen uptake. It can also be deduced from the work that the HSC of the SiCx fibers could be further increased if the crystallinity and the composition are better controlled. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.