The thermal degradation behaviour of copolymers of maleic anhydride and styrene was studied by pyrolysis-gas chromatography and thermogravimetry. The main decomposition products analysed in the temperature range 200-600 degrees C are styrene, benzene, toluene and ethylbenzene, the proportions of which vary with temperature and the nature of the copolymer. The experimental techniques used allowed a differentiation to be made between the copolymers analyzed. The apparent thermal stability of maleic anhydride-styrene copolymers is lower than that of polystyrene and decreases in the order : alternating, random and block.