The ultimate goal of this study was to further improve tensile properties of continuous bundles of highly aligned carbon nanofibers. The hypothesis was that adopting moderate tension during carbonization could improve the formation and orientation of graphite crystallites, leading to increased tensile properties of carbon nanofibers. In this study, bundles consisting of highly aligned PAN copolymer nanofibers were first prepared by electrospinning and collected via a flowing water bath, followed by 3-time stretching and oxidative stabilization. The stabilized PAN nanofibers were then carbonized under tensions of 10-50 cN which corresponding to 254.7-1273.5 MPa, respectively. The effects of carbonization tension on structural and tensile properties of carbon nanofibers were investigated by WAXD, Raman spectroscopy and filament specimen methods. The results indicated that the orientation of graphite crystallites in carbon nanofibers could be improved by increasing carbonization tensions from 254.7 MPa to 509.4 MPa; and the highest tensile strength and modulus of carbon nanofibers could reach 1115 MPa and 194.5 GPa, respectively. (C) 2016 Elsevier B.V. All rights reserved.