Nanozirconia (nano-ZrO2) was prepared by the sol gel method and incorporated into poly(methyl methacrylate) (PMMA) by the in situ bulk polymerization of methyl methacrylate. The structure of the nano-ZrO2 was confirmed by X-ray diffraction (XRD), transmission electron microscopy, and Fourier transform infrared (FTIR) spectroscopy. The structure of the nano-ZrO2 nanocomposites were studied by differential scanning calorimetry, FTIR spectroscopy, XRD, and scanning electron microscopy, and the results show that there were interactions between the nanoparticles and the polymer. The influence of the nano-ZrO2 on the thermal stability of PMMA was investigated by thermogravimetric analysis (TGA). The results indicate that nano-ZrO2 enhanced the thermal stability of the PMMA/nano-ZrO2 nanocomposites. The effects of the heating rate in dynamic measurements (5-30 degrees C/min) on kinetic parameters such as apparent activation energy (E-a) in TGA both in nitrogen and air were investigated. The Kissinger method was used to determine E-a for the degradation of pure PMMA and the PMMA/nano-ZrO2 nanocomposites. The kinetic results show that the values of E-a for the degradation of the nanocomposites were higher than that of pure PMMA in air. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 163-170, 2010