The kinetics of the disproportionation reaction of tin(II) oxide (SnO) to tin(IV) oxide (SnO2) and tin metal (Sn) was studied ex-situ and in-situ by X-ray powder diffraction with synchrotron radiation. Depending on sample preparation and decomposition temperature, an intermediate oxide Sn2O3 was observed. From thermal disproportionation at different temperatures, we extracted the reaction rate law and the reaction rate coefficients k and activation energy E-A for the disproportionation of SnO and Sn2O3. The reaction follows a nucleation and growth mechanism according to Avrami-Erofeyev with a reaction exponent m = 2. At low temperatures, a synchrotron radiation-induced disproportionation of SnO was observed. (C) 2004 Elsevier B.V. All rights reserved.