The tensile properties of electrospun fibers have not been widely investigated due to the difficulties in handling nanofibers and measuring low load for deformation. In this study, the effect of dimensional confinement on free standing biodegradable poly(c-caprolactone) (PCL) is investigated using electrospinning-enabled techniques and a nanoforce tensile tester. The structural properties such as crystallinity and molecular orientation of the spun fibers are examined using wide angle X-ray diffraction (WAXD). The degree of crystallinity and molecular orientation of fibers are enhanced when the diameter of spun fibers is reduced, resulting in improved mechanical strength and stiffness. It is evident that PCL fibers with decreasing fiber diameter exhibit an abrupt shift in tensile performance in comparison to those derived from non-spun systems. The abrupt shift in tensile strength and stiffness of electrospun PCL fibers occurs at around 700 nm in diameter and illustrates the importance of studying the mechanical behavior of the nanofibers, for the first time, systematically with the aid from electrospinning techniques. This shift cannot be otherwise explained by a noticeable change in T-g, and the gradual increase in crystallinity and molecular orientation. (C) 2008 Elsevier Ltd. All rights reserved.