The terpolymer (2,4-DHACF) synthesized from the polycondensation of 2,4-dihydroxyacetophenone and catechol with formaldehyde in an acidic medium. The terpolymer was characterized by UV-Visible spectra, FTIR and NMR spectroscopy. The thermal stability of the polymer was determined by TGA. In addition, the activation energy for the formation of terpolymer resin was calculated using TGA data by Freeman-Caroll method and Sharp-Went-worth method. Thermal activation energy (Ea) calculated with above two methods are in close agreement. The surface features of the polymer were analyzed by scanning electron microscopy (SEM). The thermodynamic parameter such as free energy change (ΔF), entropy change (ΔS), Apparent entropy change(S*) and frequency factor Z are also determined on the basis of TGA curve and by using data of Freeman-Carroll method.