Solutions of two biodegradable polymers, that is, poly(DL-lactic acid) (PDLLA) and poly(3-hydroxy butyrate) (PHB), were individually delivered to the inner and outer channel of a coaxial-tube spinneret for electrospinning to prepare core-shell fibers used for drug release applications. By interchanging the inner- and outer-channel solutions, either PDLLA/PHB or PHB/PDLLA core-shell fibers could be conveniently obtained. Their fiber diameters were readily controlled by the flow rate of the core fluid (Q(c)). The effects of Q(c) on the morphologies of the Taylor cone, the whipping jet, and the electrospun fibers were investigated. Several scaling laws describing the Q(c) dependence of the outer fiber diameter (D-f) and the inner fiber diameter (d(f)) were derived, that is, D-f similar to Q(c)(0.02) and d(f) similar to Q(c)(0.18) for the PDLLA/PHB fluids and D-f similar to Q(c)(0.30) and D-f similar to Q(c)(0.59) for the PHB/PDLLA fluids. These scaling laws provided the processing guidelines for the manipulation of the final diameters of the core-shell fibers for a given pair of electrospinning solutions. The microstructure revealed by differential scanning calorimetry, Fourier transform infrared spectroscopy, and wide-angle X-ray diffraction showed that the PDLLA component was in the amorphous state. In addition, the crystallizability of the PHB component remained relatively unchanged despite the reduction of its measured melting enthalpy when the PDLLA content was increased through an increase in its flow rate. By controlling Q(c), PDLLA/PHB fibers with a PHB shell of a similar crystallinity but with different thicknesses were readily obtained and used for the sustained release of dimethyloxalylglycine (DMOG) drug, which is a proangiogenic compound acting via the hypoxia-inducible factor system. In contrast with the singlecomponent PDLLA and PH B fibers, which exhibited a burst release behavior, two-stage release kinetics was observed for the present PDLLA/PHB fibers when DMOG was embedded in the core section: an initial fast release before the inflections followed by a constant release. For the first stage, the amount released was similar to 25% within 60 h, irrespective of the PH B thickness. After the burst release, DMOG was linearly released up to an amount of 70%, and the release rate was feasibly controlled by the thickness of the PHB shell.