The oxidative thermal decomposition of natural tetradymite (Bi2STe2) has been studied by thermal techniques and by X-ray diffraction, infrared spectroscopy and scanning electron microscopy. Oxidation occurs exothermically at comparatively low temperatures, whereas desulfatization takes place endothermically at higher temperatures. A scheme for the overall reaction is proposed. The exothermic process occurs at lower temperature for material of smaller particle size.