Studies on the isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) nucleated with anhydrous sodium acetate were carried out. The nucleated agent had succeeded in promoting greater rates of crystallization in PET. A study of the melting behavior of the samples revealed that the nucleating agents promoted formation of thinner lamellae. The equilibrium melting temperature (T-m(0)) of samples was determined using linear and nonlinear Hoffman Weeks procedure. The nonlinear Hoffman Week's procedure was found to be inapplicable in the current study. The Lauritzen-Hoffman secondary nucleation theory was applied to determine the nucleation parameter (K-g), fold surface energy (sigma(e)), and work of chain folding (q). sigma(e) and q decreased on addition of nucleating agent. The approximate and exact form of the Lauritzen Z-test was used to determine the operating regime. The operating regime was found to be primarily regime II for the range of temperatures studied. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 3541-3554, 2010