We prepared iron-impregnated silica films, which turned out to be very efficient catalysts for carbon nanotube synthesis, by a sol-gel process starting from the mixture of tetraethyl orthosilicate (TEOS), aqueous solution of iron nitrate (Fe(NO3)(3)(.)9H(2)O), and ethanol. The Fe/silicate-composite catalyst films consisted of nanoparticles, the composition and diameter of which depended on the iron-nitrate molarity in aqueous solution. Within the range of 0.5-1.5 M, the nanocomposite particles maintained good catalytic capacity, and very long and dense bundles of multimall carbon nanotubes were synthesized regardless of the iron-nitrate molarity. The carbon nanotube density was so high that the nanotube bundles appeared made of aligned nanotubes in spite of the curliness of the individual nanotubes. However, carbon nanotubes were scarcely synthesized below 0.4 M of iron-nitrate molarity, which we attributed to the unfavorable composition and distribution of Fe-species in nanocomposite particles. (C) 2004 American Vacuum Society.