In this study, polyvinyl alcohol (PVA) and gelatin are coaxially electrospun into core shell nanofibers to derive mechanical strength from PVA and bioactivity from gelatin. The core shell nanofibers with PVA in the core and gelatin in the shell display an increased Young's modulus, improved tensile strength, and reduced plastic deformation than PVA nanofibers. When the order of gelatin and PVA is reversed in the core shell nanofibers, however, the mechanical strengthening effects disappear. It thus suggests that the bioactive yet mechanically weak gelatin shell improves the molecular alignment of PVA in the core and transforms the weak, plastic PVA into a strong, elastic PVA. The use of a gelatin shell as a biological coating and a protecting barrier to strengthen the core in electrospinning presents a new strategy for fabricating advanced composite nanofibers. (C) 2013 Elsevier Ltd. All rights reserved.