The thermal degradation behaviour of polyacrylate and its zinc oxide composites were investigated by differential scanning calorimetry (DSC), thermogravimetry (TG) and Fourier transform infrared spectroscopy (FTIR). Reaction mechanisms of polymer degradation with and without ZnO particles were obtained. Filler-free polyacrylate exhibited one DSC peak, indicating that the polymer was degraded with only one stage of weight loss. Polyacrylate/ZnO composites underwent two minor weight losses as well as the major weight loss. ZnO stabilized or destabilized the polymer molecules according to the temperature region. Two mechanisms were proposed for the change of thermal properties of the nanocomposite. An increase of the stabilization or destabilization effect of ZnO nanoparticles was found in the nanocomposite with a higher content of the inorganic phase. Compared to micron ZnO particles, ZnO nanoparticles exhibited a greater effect due to their high specific area giving more sites for interactions. In addition, kinetics of thermal degradation of filler-free polyacrylate and polyacrylate/ZnO composite were quantitatively obtained by means of non-isothermal weight loss data analysis.