The effects of alignment of polyacrylonitrile (PAN) nanofibers and a two-step drawing process on the mechanical properties of the fibers were evaluated in the current study. The alignment was achieved using a high-speed collector in electrospinning synthesis of the nanofibers. Under optimal two-step drawing conditions (e.g., hot-water and hot-air stretching), the PAN nanofiber felts exhibited large improvements in both alignment and molecular chain-orientation. Large increase in crystallinity, crystallite size, and molecular chain orientation were observed with increasing draw ratio. Optimally, stretched PAN-based nanofibers exhibited 5.3 times higher tensile strength and 6.7 times higher tensile modulus than those of the pristine one. In addition, bulk density of the drawn PAN nanofibers increased from 0.19 to 0.33 g/cm(3). Our results show that fully extended and oriented polymer chains are critical in achieving the highest mechanical properties of the electrospun PAN nanofibers. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43945.