The preparation of nano poly(phenylsilsesquioxane) particles (nano-PPSQ) and the influence of nano-PPSQ on the thermal stability and crystallization of polypropylene (PP) were studied. The morphology and thermal stability of PP/nano-PPSQ composites were characterized by scanning electron microscopy (SEM) and the thermogravimetric analysis (TGA). The SEM result showed that the particles were well dispersed in the PP matrix. The TGA results of the PP/nano-PPSQ composites indicated that the incorporation of nano-PPSQ can improve the thermal stability of PP. The crystallization behavior and kinetics of PP/nano-PPSQ composite were studied by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The XRD revealed that the addition of nano-PPSQ influences the crystallinity and crystal size of PP. The Avrami, Ozawa, and combined Avrami/Ozawa (Mo method) equations were applied to describe the crystallization kinetics and estimate the kinetic parameters of mathematical models under the nonisothermal crystallization of PP and PP/nano-PPSQ composites. The results show that nano-PPSQ influences the crystallization temperature and rate. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 995-1003, 2011