This paper deals with the thermal and thermal-oxidative degradation of pure poly(methyl methacrylate) (PMMA), PMMA/AlN and PMMA/Al2O3 composites. Kinetic parameters were determined from the weight loss data using non-isothermal Thermogravimetric Analysis (TGA). The amount and morphology of the carbon residue in the burnt samples under N-2 and air atmospheres were also investigated using a Leco combustion analyzer. This study also showed that the normally accepted three-stage polymer thermal degradation, and hence three regions of Arrhenius linearity, can be treated with one value of activation energy. This is a basic departure from the normally accepted three different regions and applying the same diffusion equation (such as Jander diffusion) separately to each region. In nitrogen atmosphere, the activation energy of pure PMMA was 129.4 kJ/mol; however, the activation energies of 14% PMMA/AlN and PMMA/Al2O3 were found to be 119.5 and 118.2 kJ/mol, respectively.