Background: Terpolymer having versatile applications in adhesives, electroluminescent devices, packaging, coating materials, ion exchanger and hardener for epoxy resin. Objective: In the present investigation, our main aim was to synthesize terpolymer using 8-hydroxyquinoline-5-sulphonic acid, anthranilic acid and formaldehyde (8-HQ-5-SAAF) via polycondensation method and to evaluate thermal properties of terpolymer. Results: TGA analysis shows that the synthesized terpolymer resin was thermally stable. The activation energy calculated by Freeman-Carroll and Sharp-Wentworth methods has been found to be in good agreement with each other. The low value of frequency factor and negative entropy value indicates that the thermal decomposition would be a slow reaction. Conclusion: The thermal energy of activation calculated by using Sharp-Wentworth and Freeman-Carroll methods are found to be nearly identical. The terpolymer 8-HQ-5-SAAF starts degradation at high temperature, showing that this polymer resin is thermally stable.