Abstract: The present paper covers the isothermal crystallization kinetics of PET with different mol.wt.that were got by solid state polycondensation.The experimental result shows that in the case of solid state polycondensation no matter whether the crystallization process begins from the melt state or from the glass state, the isothermal crystallization process in later stage can be described well by modified Avrami equation.t₀ (the collision time of spherulites), t_1/2 as well as the isothermal crystallization rate are discussed.Furthermore, the influences of mol.wt.of PETand temperature on the crystallization rate was also studied.The results also show that the crystallization rules of PETgot from solid state polycondensation are basically the same as that of samples got from melt polycondensation.

Key words: Solid state polycondensation, PET, Isothermal crystallization kinetics