Carbon nanofibers (CNFs) were prepared on Ni metal catalyst at 500degreesC by thermal CVD using acetylene as a carbon source in fixed bed reactor. To obtain pure CNFs without metal catalyst, as-prepared CNFs were treated in hot nitric acid. The morphological changes for as-prepared and nitric acid treated CNFs were investigated by means of SEM and TEM. After this purification process, the eliminated Ni particles using catalyst of CNFs growth was explained by TGA analysis. The improved discharge capacity attributed to the hydrogen storage amount was systemically discussed in terms of the elimination of metal catalyst by CNFs purification in hot nitric acid. (C) 2002 Published by Elsevier Science Ltd on behalf of the International Association for Hydrogen Energy.