The present paper deals with a systematic investigation of the lime reactivity against sulfur dioxide. All experiments were performed thermogravimetrically under isothermal conditions, within a temperature range of 998- 1300 K on samples of lime with main diameters of granules between 0.04 and 1.425 mm. The content of active calcium oxide against hydrochloric acid was between 94.3-96.8 %. The graphical method applied for processing the experimental data in coordinates specific to the Avraami-Erofeev-Kolmogorov’s equation go the following mathematical model (presented in the paper).