In this article, the relation between the macrostructural changes in uniaxially stretched polyester (PET) fibers, caused by heat treatment, and quenched in coarse-grain ice were studied. The developing macrostructure was determined using double-beam interferometry. Application was carried out by two-beam interferometry to determine the optical parameters. Using a two-beam Pluta polarizing interference microscope connected to a device to dynamically study the draw ratio with birefringence changes. The relations of drawing changes with some optical parameters are given. The evaluation of density, the mean square density fluctuation, crystallinity, amorphous orientation, crystalline orientation functions, the mean square density fluctuation [eta(2)], the number of chains per unit volume N-c, and the number of random links between the network junction points N-(1) have been found. The results obtained clarify the effect of annealing time and temperature with different draw ratios on the structure of PET fibers. Also, the optical results were used to calculate an optical orientation function and an optical orientation angle of drawn, quenched PET fibers. Relations between the optical data, draw ratios, and other parameters with different quenching conditions are given for these fibers. The change of the refractive index profile of the quenched PET fibers with various conditions are given. Illustrations are given using graphs and microinterferograms.