The thermal degradation of DuoliteA-378 70.0oC, 100.0oC and 120.0oC was carried out to predict the effect of temperature on the selectivity behaviour of DuoliteA378towards anions like iodide and bromide. The equilibrium constant K values for the ion exchange reactions at different degradation temperatures of 70.0oC, 100.0oC and 120.0oC were calculated at different temperatures from which the standard enthalpy, standard entropy and standard free energy values were obtained. The standard enthalpy values of the above ion exchange reaction performed by using fresh and degraded resins Duolite A378 at 70.0oC, 100.0oC and 120.0oC were calculated as-40.15,-27.28,-44.89,-76.71kJ/molefor Cl-/I- and for Cl-/Br-were-31.23,-53.72,-82.14,-34.59kJ/mole respectively. The results obtained from the study shows that iodide ions were easily exchange towards the resin surface compared to bromide ions. The degradation of resin surfaces characterised and identified with help of SEM and IR.