High-speed melt spinning of single and bicomponent fibers of poly ethylene terephthalate (PET) and nylon 6 was carried out. The structure changes in the individual components of the single and bicomponent fibers with take-up velocity were investigated by birefringence, wide-angle x-ray diffraction, and DSC. The orientation crystallization of PET in the bicomponent fiber was enhanced in comparison with the pure PET fiber, while the orientation of the PET component increased with decreasing the PET content. On the other hand, the orientation of the nylon 6 component was lower than that of the corresponding single component fiber. The cold crystallization temperature of PET in the bicomponent fiber was lower than that of the pure PET fiber. It was also lowered with decreasing PET content. The crystal formation of PET in the bicomponent fiber occurred at a lower take-up velocity than that of the pure PET fiber. In high speed spinning, neck-like deformation was also observed in the bicomponent spinning. The neck-like deformation of PET occurred at a position closer to the spinneret than that of nylon 6, mean-while the position of the neck-like deformation of the 1:3 bicomponent fiber was observed at a position closer to the spinneret than that of the pure PET fiber.