The interest in fabrication of nanofibers using electrospinning method has attracted considerable attention due to its versatile maneuverability of producing controlled fiber structures, porosity, orientations and dimensions Although the process appears to be simple and straightforward, an understanding of the technique and its influence on the morphology, structural and mechanical properties is still not completely clear Recently, the size effect on the mechanical properties was reported for fibers across different length scales Both modulus and strength of poly(epsilon-capro-lactone) (PCL) fibers were found to Increase significantly when the diameter of the fibers was reduced to below similar to 500 nm In this article, for the first time, we critically review and evaluate the role of the microstructures on the fiber deformation behavior and present possible explanations for the enhanced properties of the nanofibers Our discussions are focused on the techniques to obtain controlled structures and the mechanisms behind the size effect in electronspun fibers are given In-depth understanding of these mechanisms can provide fruitful outcomes in the development of advanced nanomaterials for devices and miniaturized load-bearing applications (C) 2010 Elsevier Ltd All rights reserved