Poly(butylene terephthalate) fibers were prepared by high speed melt spinning in the range of 4~8 km/min and annealed under various conditions. The efforts of annealing temperature and tension on the fine structure and properties of PBT fibers were investigated using density, birefringence, WAXD, TMA, tensile test, etc. In the case of PBT fiber annealed under taut conditon, the results of WAXD profiles indicated that (100) plane was inclined relative to the fiber axis, and we confirmed that the reflection peak varied with the inclination of the fiber axis from 2$^{circ}$ to 8$^{circ}$ In the TMA results of PBT fibers annealed at various temperatures, shrinkage tendency suggested that crystallization prevailed over chain re-coiling. In the s-s curves results, the elongation of the PBT fibers annealed below 10$0^{circ}C$ is increased and the specific stress is similar. Especially, in the case of PBT fiber spun at 4 km/min, higher annealing temperatures resulted in an increased work of rupture.