The nonisothermal crystallization kinetics of polypropylene (PP), PP/polystyrene (PS), and PP/PP-g-PS/PS blends were investigated with differential scanning calorimetry at different cooling rates. The Jeziorny modified Avrami equation, Ozawa method, and Mo method were used to describe the crystallization kinetics for all of the samples. The kinetics parameters, including the half-time of crystallization, the peak crystallization temperature, the Avrami exponent, the kinetic crystallization rate constant, the crystallization activation energy, and the F(T) and a parameters were determined. All of the results clearly indicate that the PP-g-PS copolymer accelerated the crystallization rate of the PP component in the PP/PP-gPS/PS blends. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 1721-1731, 2011