Copolymer resins (8-HQ-5-SAUF) were prepared by the condensation of 8-hydroxyquinoline 5-sulphonic acid, urea and formaldehyde in the presence of hydrochloric acid as catalyst with varying the molar ratio of reacting monomers. Compositions of copolymers have been determined by elemental analysis. The number average molecular weights (Mn) have been determined by conductometric titration in non-aqueous medium. Electronic spectra, infrared spectra and nuclear magnetic resonance spectra were studied to elucidate the structure. Detailed thermal degradation study of the new copolymer resins have been carried out to ascertain its thermal stability. Thermal degradation curve is discussed which shows three decomposition steps after the loss of water molecule. Sharp-Wentworth and Freeman-Carrol methods have been used to calculate activation energy and thermal stability. The activation energy (Ea) calculated by using Sharp-Wentworth method has been found to be in good agreement with that calculated by Freeman-Carrol method. Thermogravimetric parameters such as free energy change (DG), entropy change (DS), apparent entropy change (DF), frequency factor (Z) have also been evaluated on the basis of the data of Freeman-Carrol method. The order of reaction (n) is found out to be 0.99.