The crystallization kinetics of pure poly(butylene terephthalate) (PBT) and toughed modification PBT/polycarbonate (PC) blends with ethylene-butylacrylate-glycidyl methacrylate copolymer (PTW) and ethylene-1-octylene copolymer (POE) were studied. For nonisothermal crystallization process studies, the Ozawa theory and an equation combining the Avrami and Ozawa equation are used. It is found that the Ozawa analysis fails to provide an adequate description of the nonisothermal crystallization process in PBT, PBT/PC, and toughed PBT/PC blends, while the combination of the Avrami and Ozawa equations exhibit great advantages in treating the nonisothermal crystallization kinetics. The activation energies are determined by the Kissinger method for nonisothermal crystallization. The activation energy for PBT/PC/PTW/POE blend is greater than those of PBT/PC, and PBT/PC/POE blends. Isothermal crystallization processes were studied by the Avrami equation. The results show that the values of the Avrami exponent n for PBT, PBT/PC, and toughed PBT/PC blends are 3.8, 3.0, and 2.8-3.2, respectively. The Avrami rate constant K for PBT, PBT/PC, and toughed PBT/PC blends increase in following order: K-PBT/PC < K-PBT/PC/POE < K-PBT/PC/PTW/POE < K-PBT (c) 2006 Wiley Periodicals, Inc.