The kinetics of nonisothermal crystallization of polypropylene (PP) containing nanoparticles of silicon dioxide (SiO2) were investigated by differential scanning calorimetry (DSC) at various cooling rates. Several different analysis methods were used to describe the process of nonisothermal crystallization. The results showed that the Ozawa equation and Mo's treatment could describe the nonisothermal crystallization of the composites very well. The nano-SiO2 particles have a remarkable heterogeneous nucleation effect in the PP matrix. The rate of crystallization of PP/nano-SiO2 is higher than that of pure PP. By using a method proposed by Kissinger, activation energies have been evaluated to be 262.1, 226.5, 249.5, and 250.1 kJ/mol for nonisothermal crystallization of pure PP and PP/nano-SiO2 composites with various SiO2 loadings of 1, 3, and 5%, respectively. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1013-1019, 2004.