Studies of non-isothermal decomposition of some new diarylidene-isopropylpipridinone polyesters were carried out using TGA measurements in air atmosphere. TG and DTG investigations revealed that the decomposition of these polymers proceeds in four stages. Analysis of TG curves proves the advantages of this technique in quickly providing valid information about the thermal decomposition kinetics of the polymers. The kinetic parameters such as activation energy E(a), pre-exponential factor A, entropy of activation S*, free energy of activation G and enthalpy of activation H for all polymers at different decomposition stages are determined. The data show that the thermal stabilities of these polymers are in the order I > II > IV > III. In addition, the effect of the presence of a substituent -OCH3 group upon the thermal properties of polymers is discussed.