Abstract: The crystallization rate and tensile behavior were studied for two amorphous PET films A and B, prepared by using Sb₂O₃ and SnC₂O₄ as polycondensation catalyst respectively. It was found that sample A is more easily crystallized than sample B. Experimental results indicated that the crystallization rate is really an important factor affecting the tensile properties of PET films, and it is possible to change their processing behavior by using different catalyst.It was proposed to use area ratio at break Rb and σ₁₀, the stress value at two tensional draw ratio=10, as parameters characterizing the processibility of PET film.