Poly(3-hydroxybutyrate) (PHB) is a bio-based polyester, however, melt-processing of PHB is difficult since thermal degradation starts near its melting temperature. PHB copolymerized with 3-hydroxyhexanoate (3-HH) is one of the co-polyesters developed to overcome such difficulty, however, processing of this polymer (PHBH) still is not easy because the Tg of PHBH is below the room temperature, whereas the crystallization rate is quite low. Accordingly, it is difficult to form fibers, films and other products through the melt processing because the polymer can be still in a rubbery state after cooling to the room temperature. In this research, attempts were made to overcome such difficulty by applying the high-speed melt spinning process. In this process, high tensile stress applied to the spin-line leads to the development of molecular orientation and orientation-induced crystallization. Along with the effect of take-up velocity, effects of the extrusion temperature and through-put rate were investigated for two types of PHBH with different 3-HH content. In the melt spinning of high 3-HH content PHBH, fibers stuck together on the bobbin because crystallization did not occur in the spin-line. There was a slight indication of the starting of crystallization in the spin-line under only limited conditions. In case of the low 3-HH content PHBH, crystallization occurred when extrusion temperature was lower than the melting temperature of pure PHB. Structure development behavior was also affected by the through-put rate since the degree of thermal degradation varied depending on the residence time in the extruder. At relatively high extrusion temperatures, fiber spinning was successful at low and high take-up velocities, whereas in the medium take-up velocities, it was difficult to obtain fibers. This was considered to be due to the crystallization of the fibers of medium level of molecular orientation on the bobbin which accompanies the spontaneous elongation of the fibers.