Ultrafine polylactic acid (PLA) based fibers were fabricated via a home-built melt electrospinning device. To improve the spinnability and reducing the fiber diameter, PLA was melt-compounded with polyethylene glycol (PEG) at different concentration ranges from 0 to 30 wt% in a batch internal mixer. Obtained PLA/PEG samples were characterized through dynamic rheometery and differential scanning calorimetry (DSC). Accordingly, an intense reduction of viscosity, relaxation time of polymer chains, and enhancement of chain mobility due to plasticizing effect of PEG were observed. Then, by manipulation of applied electric filed, spinning temperature, nozzle to collector distance, and PEG content, PLA fibers of various diameters were melt spun and optimized spinning conditions was achieved. Fiber diameters and surface morphology were studied using optical (OM) and scanning electron microscopy (SEM). Increasing the spinning temperature up to 230 ºC and electric field strength reduced the diameter of neat PLA fibers. While, at the optimum PEG content (20 wt %) PLA/PEG blends were easily spun at 180 ºC and the lowest fiber diameters of 2-5 μm were achieved at applied voltage of 40 kV and nozzle to collector distance of 10 cm. Hydrothermal degradation of PLA based fibers during the melt electrospinnig was less than 5% according to gel permeation chromatography (GPC). Due to rapid solidification, melt electrospun PLA fiber mats were mostly amorphous, and less significant presence of crystallinity (~ 20%) and imperfect α crystals were noticed in PLA/PEG 80/20 and 70/30 fibers by DSC and X-ray diffraction (XRD) studies.