The thermal stability of poly( N-vinyl-2-pyrrolidone-co-methacrylic acid) copolymers was studied by thermogravimetry and infrared spectroscopy in inert atmosphere. The thermogravimetric curves suggested that the effective degradation of both systems occurred in the temperature range 350–500 °C with more than 60% mass loss. At this temperature, the activation energy was in the range 160–200 kJ mol −1 (average values), suggesting that the degradation occurred by a random scission of the chain. The FTIR results indicated that the main volatile products of degradation are CO 2, CO and hydrocarbons (unsaturated structures) with low molecular weight. Pure PVP also showed the formation of NH 3 which was apparently suppressed in the copolymer by the formation of large amounts of CO 2 and CO. The results suggested that the thermal stability of the copolymers was essentially associated with the N-vinyl-2-pyrrolidone monomer, losing stability when the percentage of methacrylic acid in the copolymer system was increased.