The α→β transformation between orthorhombic (α) and hexagonal (β) polymorphs of strontium carbonate has significant effect on the behavior of SrCO 3 during thermal treatment. The kinetics, mechanism and thermodynamics of activated complex in the process of thermal decomposition were investigated by non-isothermal thermogravimetric analysis (TGA) using mechanism-free (Kissinger equation) as well as kinetic function fitting methods. Both techniques as well as the calculation of theoretical activation energy (third law method) show that the transformation of α-SrCO 3 to β-SrCO 3 reduces the activation energy and changes the mechanism of the process. While thermal decomposition of rhombohedral SrCO 3 is limited by the rate of process to the reaction interface (R 3 : g(α)=1−(1–α) 1/3 ), the process limited by the rate of chemical reaction of 1/3 order (F 1/3 : 1−(1–α) 2/3 ) was determined for the hexagonal polymorph. The samples before and after thermal treatment were investigated by infrared spectroscopy, scanning electron microscopy and X-ray diffraction analysis.