Supercritical carbon dioxide (SC CO2) was used as a carrier/solvent for the "dry" alumination of mesoporous silica to prepare aluminium-containing mesoporous MCM-41. The effect of alumination on the structure and crystallinity of the materials was studied. In addition, the hydrothermal and thermal stability of this material have been investigated and compared with Al-MCM-41 prepared via conventional impregnation and direct hydrothermal synthesis. Irrespective of the preparation method, the surface area, pore diameter, pore volume, and crystallinity of Al-MCM-41 all decrease after hydrothermal and thermal treatments. However, Al-MCM-41 materials prepared with the assistance of SC CO2 possess better hydrothermal and thermal stability. This method allows for the incorporation of aluminum onto rather than into pores wall, without disintegration of the mesoporous structure, compared to Al-MCM-41 that has been prepared via impregnation and direct hydrothermal synthesis.