Gels with the composition of mullite (3Al2O3-2SiO2) were prepared from an aqueous solution of aluminium oxalate and tetraethoxysilane. High-purity stoichiometric mullite powders were produced by calcination of the gel powders with a small exothermic event at 1250-degrees-C. The chemical and structural evolutions were characterized as a function of heat treatment by differential thermal analysis (DTA), thermogravimetric analysis (TGA), X-ray powder diffraction (XRD) and infrared (i.r.) spectroscopy. The composition of mullite varied with the temperature of the heat treatment.