In this study, PET (intrinsic viscosity of 1.05 dl/g) was melt processed with a horizontal isothermal bath (HIB) treatment. Tensile properties of PET fiber samples were highly increased by using the HIB. The process-structureproperty relationship of control (no HIB) and HIB fiber samples were characterized by tensile testing, differential scanning calorimetry, birefringence measurement, scanning electron microscopy and hot-air shrinkage measurements. It was found that HIB fiber samples, which had been subjected to post-drawing process, had a high degree of molecular chain orientation, that is, a high birefringence, high crystallinity and a fibrillar structure. The best tensile property acquired from a HIB-drawn PET fiber sample was 10.24 g/d in tenacity, 114.17 g/d in modulus, and 13.49% in elongation at break. Applying the HIB in the melt spinning process was simple and required only small process space; hence, it is cost effective. In addition, acquiring HIB fiber samples was successful at a final take-up speed of 2,500 m/min. Hence, this HIB-assisted melt spinning technology has a high potential to be used in industries for technical textiles applications. POLYM. ENG. SCI., 57: 224-230, 2017. (C) 2016 Society of Plastics Engineers.