Polyvinylidene fluoride (PVDF) fibers with a high amount of phase crystal structure were prepared by melt spinning. With this technique, the cold drawing process is critical and efficient when aiming for a high amount of phase. During the cold drawing process, more than 80% of the originally formed phase crystal structure was converted into the phase structure. In addition, the incorporation of 0.01 wt % of amino-modified double wall carbon nanotube (NH2-DWCNT) could further enhance the phase content in the PVDF fibers. FTIR and DSC studies showed that the addition of NH2-DWCNT to PVDF fibers could increase both the total crystallinity and phase fraction in PVDF. The addition of nanoclay was found to be less efficient in this respect. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2603-2609, 2013