Poly(ethylene terephthalate) is a dominant synthetic fiber for garment and it occupies 85% of synthetic fiber products, and is the most encountered single fiber during the trace physical evidence identification. For the single fiber identification, chemical analyses play a significant role. In this experiment, we focused on the physical properties, such as, their orientation and inorganic additives. We applied the discrimination of poly(ethylene terephthalate) by observation of the intensities profile of polarized light and scattering light near the melting points with the polarized microscope and accurately temperature controlled hot plate. Poly(ethylene terehthalate) was put cross Nicole position. Most of the samples showed the similar profile of poly(ethylene terephthalate) to the poly(ethylene terephthalate) mixed with cotton. The intensity profile was stronger than that of intensity before melting, but several samples did not show these phenomena. In regard with the orientation, light profiles were different in low, medium and high oriented poly(ethylene terephthalate) fibers. As an addition of inorganic compound, Kaolin made the melting point higher than other samples. In many cases, TiO₂ was added as preparing dull fibers, in this experiment, sufficient reproducibility was not obtained in these samples, but morphological observation could discriminate at 0.05% of adding of TiO₂ to fiber. The fibers with this amount of TiO₂ added could not be distinguished by chemical analysis by widely used infrared spectroscopy. In the recycled poly(ethylene terephthalate) fiber, the polarizing light intensity was weak. These results indicate not only chemical analysis but also measuring the physical property and morphological observation are also effective for the forensic discrimination of fibers.