The thermal decomposition of pure perspex and a mixture of 50% perspex and 50% poly(ethylene terephthalate; PET) was carried out between 295 and 325 degrees C using a thermogravimetric analyser (TGA) in air and nitrogen (N2) atmosphere. The weight losses of decomposition products were measured during these experiments. The thermal degradation process is slower in inert atmosphere than air, where oxidation reaction expedites the decomposition process. Kinetic rate constants (k), pre-exponential factor (A) and activation energy (E) for both pure prespex and a blend of perspex/PET were calculated for both air and N2 conditions. The thermal degradation process followed a third-order reaction in air and second-order in N2. A second-order (n=2) model for the pyrolytic process based on simultaneous reactions was developed using experimental data for pure and blend. The pyrolytic products are gases, liquids, waxes, aromatics and char, which can be ultimately used as raw material and fuel in various applications. It is important to note that the addition of PET to perspex was found to suppress/inhibit the decomposition of perspex compared with pure perspex. Pre-exponential factor (A) and activation energy (E) values support such an observation. (c) 2012 Canadian Society for Chemical Engineering