The thermal decomposition and kinetic parameters of synthetized imatinib mesylate α form α form were determined by thermogravimetry (TGA/DTG) under non-isothermal conditions. The experiments were performed at a 25–940 °C temperature range at five different heating rates: 2.5 K min−1, 5 K min−1, 10 K min−1, 15 K min−1 and 20 K min−1 per minute in a nitrogen atmosphere. Imatinib mesylate α form presents one-step mass loss during the degradation process. The thermal stability of the examined material, the melting temperature (Tonset = 220.6 °C) and ΔH fusion = −95.74 J g−1 at a heating rate of 10 °C min−1 was established. The values of activation energies have been estimated using Kissinger, Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) methods.