Poly(ethylene terephthalate) (PET) is the most important and widely used fiber material nowadays. Even though the development of PET fiber was achieved long time ago, its tensile strength as well as the ratio of tensile strengths of the available fibers to the theoretical values are not high enough in comparison with other high-strength fibers in the market. It has been considered that the control of the state of molecular entanglement is the key for the improvement of mechanical properties. In this study, various types of PET fibers were prepared through the conventional melt spinning and drawing processes with modified spinning conditions and also through the high-speed melt spinning process with various spinning speeds. Correlation between higher order structure and mechanical properties of thus obtained fibers was investigated in detail. Along with the analyses of orientation and crystalline structure through the birefringence and X-ray measurements, laser Raman spectroscopy measurement was adopted to obtain information of not only the degrees of orientation and crystallinity but also the state of molecular entanglement and its distribution. Keywords: Poly(ethylene terephthalate) fibers, Raman spectroscopy, mechanical properties