The thermal degradations of methyl methacrylate-graft-natural rubber (MG) at different heating rates (B) in nitrogen were studied by thermogravimetric analysis. The results indicate that the thermal degradation of MG in nitrogen is a one-step reaction. The degradation temperatures increase along with the increment of heating rates. The temperature of initial degradation (T-0) is 0.448B + 362.4degreesC, the temperature at maximum degradation rate, that is, the peak temperature on a differential thermogravimetric curve (T-p) is 0.545B + 380.7degreesC, and the temperature of final degradation (T-f) is 0.476B + 409.4degreesC. The degradation rate at T. is not affected by B, and its average value is 48.9%; the degradation rate at Tf is not affected by B either, and its average value is 99.3%. The reaction order (n) is 2.1 and is not affected by B. The reaction activation energy (E) and the frequency factor (A) increase along with B, and the apparent reaction activation energy (E-0) is 254.6 kJ/mol.