High-speed melt spinning of biodegradable aliphatic polyester poly(butylene succinate) (PBS), and aliphatic-aromatic copolyester poly(butylene terephthalate-co-succinate-co-adipate) (PBTSA) was carried out. The effects of spinning conditions on the structural development of PBS and PBTSA fibers were investigated through the measurements on on-line velocity profile, birefringence, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry, and tensile test. Both PBS and PBTSA fibers showed well-developed crystal structure in WAXD patterns, though the deformation of the spinline continued down to the position of winding suggesting that substantial orientation induced crystallization did not occur in spinline of both cases. Increasing take-up velocity or decreasing extrusion temperature led to the enhancement of molecular orientation, crystal structure and mechanical property of both PBS and PBTSA fibers, but no distinct effect on the thermal property of those fibers. The melting temperature of PBTSA fibers was at ca. 115 degrees C, same as that of PBS fibers. Elastomeric property of hard-soft units consisting PBT A fibers leads to its good recoverability; however this behavior lowers the initial modulus and tensile strength compared with those of the corresponding aliphatic PBS fibers.