Nonisothermal crystallization behavior of poly(butylene terephthalate) (PBT) was investigated by means of differential scanning calorimetry. The nonisothermal crystallization kinetic process was analyzed and relative kinetic parameters were obtained with the Avrami and Liu-Mo equations. The results demonstrate a heterogeneous nucleation mechanism. It was found that the nonisothermal primary crystallization of PBT was composed of two courses. Course I corresponded to the two-dimensional formation process of the lamellae, and the corresponding relative crystallinity (X-t) was less than 15%. Course II was concerned with the three-dimensional growth process of the spherulite, and X-t changed from 15 to 90%. The secondary crystallization began when X-t was greater than 90%. According to the Flynn-Wall-Ozawa equation, the activation energies for course I, course II, and secondary crystallization were calculated to be -120, -210, and -100 kJ/mol, respectively. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128: 400-406, 2013