Little is understood on the deformation of electrospun nanofibers. This study aims to evaluate the electrospun nanofiber deformation in both macroscopic and nanometer length scales using the classical hyperelastic models. The Mooney-Rivlin models are used to evaluate the tensile properties of poly(?-caprolactone) (PCL) made by the electrospinning technique. The stress-strain relationships of single fibers are reported. This study also provides comparative analyses among Mooney-Rivlin models. Analytical calculations illustrate the importance of understanding crystallinity and molecular orientations of nanofibers.