Poly(acrylamide sulfone)s are products of copolymerization of acrylamide (Aa) and sulfur dioxide (S), and form a variable composition polysulfone with average Aa:S molar ratio n⩾1.0 Their thermal degradation has been studied by thermogravimetry. The experiments were carried out over the temperature range 450–800 K at three heating rates i.e. 5, 10, 20°C/min in nitrogen. The results indicated that the entire degradation under our experimental conditions consists of two distinctive pyrolysis stages. The activation energy was evaluated from experimental thermogravimetric and differential thermogravimetric curves. The activation energies in the first stage of thermal degradation decreased with an increase in sulfur content and there was a slight difference in the second stage of thermal degradation. Slight differences have been found in activation energy depending on the analytical method used. An experimental relation between residue weight fraction and temperature is proposed for describing the thermal degradation of poly(acrylamide sulfone)s. The experimental data and the equation appear to be in good agreement.