High-speed melt spinning of sheath-core type bicomponent fibers was performed and the change of fiber structure with increasing take-up velocity was investigated. Two kinds of polymers, high molecular weight poly(ethylene terephthalate) (HMPET, [η]=1.05 dl/g) and low molecular weight poly(ethylene terephthalate) (LMPET, [η]=0.62 dl/g), were selected and two sets of sheath/core combination, HMPET/LMPET and LMPET/HMPET were studied. The structure and properties of bicomponent fibers spun with high-speed were analyzed through the density, birefringence, wide-angle X-ray diffraction, DSC, and stress-strain measurements. In high speed spinning, the HMPET component attained a higher degree of orientation than that of LMPET component, wherever it was placed in a sheath or core. The orientation-induced crystallization in HMPET/LMPET bicomponent fibers made by high-speed spinning was significantly enhanced and it amounted that of the LMPET/HMPET bicomponent fibers with take-up velocity of 4-5 km/min. The amorphous orientation factor of HMPET/LMPET bicomponent fibers were always higher than those of LMPET/HMPET bicomponent fibers. Therefore the mechanical properties of HMPET/LMPET bicomponent fibers were better than those of LMPET/HMPET bicomponent fibers.