We demonstrate that single wall carbon nanotubes (SWCNTs) can be coated by a layer of silica through the reaction between chlorosilane and acid-treated SWCNTs. The presence of carboxylic acid groups in the SWCNTs provides the active sites where chlorosilane can be anchored to form the silica coating. Silica nanotubes with diameters ranging from 5 to 23 nm were synthesized after the calcination of silica coated SWCNTs at 900 degrees C in air. It was found that the presence of SWCNT templates and carboxylic acid groups on the SWCNTs surface is essential to the formation of silica nanotubes. Furthermore, the dependence of the inner diameters of the silica nanotubes on the diameters of bundled or isolated SWCNTs was observed. This novel technique can be applied to the synthesis of other oxide nanotubes if a precursor such as TiCl(4) or ZrCl(4) is used.