Novel Al-doped six-membered ring silica nanotubes have been studied by using density functional theory. Four different Al-doped silica nanotubes are taken into account. The results indicate that Al-doped silica nanotubes still retain quasi-tube forms. A symmetry breaking of the HOMO and LUMO is observed for Al-doped silica nanotubes. These Al-doped silica nanotubes have smaller HOMO-LUMO energy gaps than that of pure silica nanotube. Al-doped silica nanotubes have a peak at around 900 cm (1) ascribed to Al-O vibrational mode, which is in good agreement with experimental and theoretical results. (C) 2010 Published by Elsevier B. V.