The uni-axial stretching of amorphous poly (ethylene terephthalate) (PET) film has been studied in the tcmperature range of 78一112℃ bv means of the temperature scanned dynamical mechanical loss curve of the stretched film．Amorphous PET films stretched at lower temperatures were crystalline，caused solely by straininced crystallization which took place when the stress-train curve stated to show an incease (strain hardening) after yielding．Amorphous tilms stretched at higher temperatures，arround 90℃ or higher，remained amorphous and optically isotropic．The latter resulted from complete relaxation of the Iocal chain orientation during hot streching．while the global orientation of the chain could only be relaxed by rubbery flow which would be rather slow．The thermal relaxation of the g lobal chain orientation have been studied by stress relaxation of the stretched amorphous film with fixed ends．At lower temperatures the films after almost complete relaxation remained amorphous．At higher temperatures the film started to crystallize during stress relaxation after the stress had relaxed to a value below 10％ of the initial stress．FTIR studies showed that this stressrelation time corresponds to the induction period of crystallization under such conditions．