Introduction: Electrospinning is a powerful and versatile process for producing polymeric fibers with micro- and nanosize diameter. High porosity and surface-area-to-volume ratio, similar morphology to the natural extra-cellular matrix, degradability, biocompatibility and mechanical strength make electrospun polymer fibers the perfect candidate for engineering of soft tissues. Electrospun fibers produced from biodegradable synthetic polymers like PLGA are potentially useful for clinical applications because their degradation products are resorbed through the metabolic pathways. However, lack of functional groups in their chemical structure for grafting bioactive cell-responsive peptides, their inability to crosslink in-situ, and their hydrophobic nature have limited their application in tissue regeneration. The objective of this work was to determine the effect of in-situ crosslinkable amphiphilic poly(lactide-co-glycolide ethylene oxide fumarate) (PLGEOF) macromer on size and morphology of the electrospun fibers produced from bimodally distributed PLGEOF/PLGA mixtures. The high molecular weight PLGA provides elongational viscosity to prevent the break up of the accelerating jet inside the electric field while the low molecular weight PLGEOF macromer provides hydrophilicity, sites for covalent attachment of cell-responsive peptides, and sites for crosslinking of fibers. Methods: Amphiphilic PLGEOF was synthesized by condensation polymerization of the ULMW PLGA, PEG, and fumaryl chloride. A programmable syringe pump was used to transfer the polymer solution to the end of a needle at a flow rate of 7.0 ml/h. The positively charged Pt electrode of a high voltage supply was connected to the end of the needle. An aluminum plate connected to the ground electrode was used as the collector. The force generated by the high electric field (25 kV) between the needle and collecting plate overcame the surface tension of the polymer solution and stretched the accelerating jet as fibers toward the collector while the solvent evaporated during the process. To produce aligned fibers, the fibers were collected on a wheel rotating at speeds ranging from 1K-2K rpm. Results: The addition of amphiphilic PLGEOF macromer to PLGA had a significant effect on size and morphology of the electrospun nanofibers. Droplets formed when 5 wt% PLGA was electrospun without the addition of PLGEOF. With the addition of PLGEOF macromer to a 5 wt% PLGA solution, the morphology of the electrospun fibers changed from bead-to fiber-like. Furthermore, when PLGEOF was added to a 12 wt% PLGA solution, the fiber diameter changed from 5.5±2.5 µm for the sample without PLGEOF to 2.2±1.1, 3.2±1.5, and 4.5±1.8 µm, respectively. The crosslinking kinetics, swelling, and degradation of the fibers were also investigated. Conslusion: Electrospun fibers made with a mixture of PLGEOF/PLGA polymers are potentially useful in fabrication of crosslinked functionalized scaffolds for tissue engineering applications.