Abstract: : Poly(L-lactide) (PLLA) and polybutyrolactam (PBL) are both biocompatible and biodegradable polymers. Here, bio-based and biodegradable fibers were electrospun from PLLA/PBL blend solutions dissolved in hexafluoroisopropanol (HFIP), the co-solvent of PLLA and PBL. The influences of PBL mass fraction on fiber properties including morphology, average diameter, thermal, crystallization and hydrophilicity properties were investigated by scanning electron microscope (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and contact angle testing. The internal structure of blend fibers was confirmed by transmission electron microscope (TEM). Dichloromethane (DCM) , the solvent of PLLA was used to etch the fibers to give a supplementary proof. It was found that beads free homogeneous fibers without band structure could be obtained from PLLA/PBL blends. The diameters of fibers distributed in a range of 0.1~1.6 μm. The average diameters of PLLA/PBL blend fibers were lower than those of pure PLLA fibers and decreased with the increasing of PBL mass fraction. The crystallinity of PLLA in as-spun fibers was low, and it could be increased by cooling from 190 °C that above the melting point of PLLA or annealing at 110 °C above its glass transition temperature. Introducing PBL into PLLA fibers hindered the melt and annealed crystallization of PLLA. The reduction in the degree of PLLA crystal perfection was characterized by the obvious decrease in either PLLA crystallization temperature during cooling or the melting temperature in the second heating. The broadening of the half-peak width of PLLA crystal diffraction peaks was another evidence provided by XRD. All evidences from TEM observation and solvent etching experiment suggested that the fibers with core-sheath structures were obtained by single-nozzle electrospinning from solutions of PLLA/PBL blends. The phase separation occurred during the electrospinning process due to various segment mobility should be responsible for the fiber structure with PBL core and PLLA sheath. It could explain why the addition of hydrophilic PBL hardly improved the hydrophilicity of as-spun fiber surfaces.