Double-walled carbon nanotubes (DWNTs) have been synthesized by catalytic chemical vapor deposition (CCVD) over supported metal catalysts decomposed from Fe(CH3COO)(2) and Co(CH3COO)(2) on mesoporous silica. Bundles of tubes with relatively high percentage of DWNTs, in areas where tubular layered structures could be clearly resolved, have been observed by transmission electron microscopy (TEM). In other areas, crystal-like alignment of very uniform DWNTs was observed for the first time, suggesting that mesoporous silica might play a templating role in guiding the initial nanotube growth. In addition, compatible with nano-electronics research, bridging of catalytic islands by DWNTs has also been demonstrated. (C) 2003 Elsevier B.V. All rights reserved.