The formation of solid solutions between tin cations and mullite by calcination at 1400degreesC of amorphous precursors prepared by pyrolysis of aerosols is reported. The oxidation state of the tin cations and the position that they occupy in the mullite structure have been analyzed using XAS (XANES and EXAFS) spectroscopy, which shows that the tetravalent tin cations are located at the octahedral positions of the Al3+ ions, which induces cell expansion. The limit of tin incorporation under the experimental conditions reported here correspond to a tin/mullite mole ratio of similar to5%, which is within the range previously reported for other tetravalent cations (4%-6%).