Abstract: The terpolymer resin 2,4-DHP-4-PAF-III was prepared by condensation of 2,4-dihydroxypropiophenone, 4- pyridylamine and formaldehyde in the presence of 2M hydrochloric acid as a catalyst in the temperature range 125 ± 2 0C for 5 hrs in 3:1:5 molar ratios of reactants. Elemental analysis, FT-IR, and 1H-NMR spectral studies have been carried out to confirm the structure of the resin. The thermal degradation behavior of terpolymer was studied using thermogravimetric analysis (TGA) in air atmosphere at a heating rate of 10 0C/min. Sharp-Wentworth and Freeman-Carroll methods were used to calculate thermal activation energy (Ea), entropy change (∆S), free energy change (∆F), apparent entropy change (S*), frequency factor (Z) and order of reaction (n). Thermal activation energy (Ea) calculated by Sharp-Wentworth (28.81 KJ/mole) method and Freeman-Carroll (29.47 KJ/mole) method are in good agreement.