Stabilization of the jet is necessary for the successful fabrication of continuous fibers from solutions via electrospinning. Although intensively studied over the past decade, the mechanisms underlying jet stabilization are still not precisely understood. The traditional explanation for jet stabilization emphasizes the role of the elastic response of the polymer coil in creating a sufficiently high extensional viscosity, which prevents the breakup of the filament under extension. However, comprehensive rheological studies of bovine serum albumin (BSA) solutions that can be electrospun into continuous fibers show an absence of any significant bulk elasticity in shear and extension that would account for the stabilization of the jet. In order to explain this discrepancy, it is proposed that a complex jet structure, composed of a liquid core surrounded by a viscoelastic interface, is formed during the spinning process, where the surface viscoelasticity is responsible for the jet stabilization. These rheological properties of the surface are experimentally verified using novel interfacial rheometry. It is also shown that the surface viscoelasticity is further enhanced by varying the protein conformation (unfolding), as well as its concentration in solution. (C) 2010 Elsevier Ltd. All rights reserved.