The thermooxiclative degradation of methyl methacrylate-graft-natural rubber (MG) at different heating rates (B) has been studied with thermogravimetric analysis in an air environment. The results indicate that the thermooxiclative degradation of MG in air is a one-step reaction. The degradation temperatures increase with B. The initial degradation temperature (T-o) is 0.697B + 350.7; the temperature at the maximum degradation rate, that is, the peak temperature on a differential thermogravimetry curve (T-p), is 0.755B + 368.8; and the final degradation temperature (T-f) is 1.016B + 497.4. The degradation rates at Tp and Tf are not affected by B, and their average values are 46.7 and 99.7%, respectively. The maximum thermooxidative degradation reaction rate, that is, the peak height on a differential thermogravimetry curve (R-p), increases with B. The relationship between B and R-p is R-p = 2.12B + 7.28. The thermooxidative degradation kinetic parameters are calculated with the Doyle model. The reaction energy (E) and frequency factor (A) change with an increasing reaction degree, and the variational trends of the two kinetic parameters are similar. The values of E and A increase remarkably during the initial stage of the reaction, then keep relevantly steady, and finally reach a peak during the last stage. The velocity constants of the thermooxidative degradation vary with the reaction degree and increase with the reaction temperature. 2003 Wiley Periodicals, Inc.