Tensile properties of gel-spun polyacrylonitrile (PAN) and PAN/carbon nanotube (CNT) fibers were studied as a function of temperature from -100 degrees C to 300 degrees C at a constant strain rate of 0.01/s. Tensile strength and modulus values at low temperature were as high as 1.65 GPa and 44.4 GPa, respectively. The tensile strength and modulus of PAN fibers decreased with increasing temperature, while drawability dramatically increased in a narrow temperature window near ala, transition temperature. Three transitions, namely, gamma, beta(c), and alpha/alpha(c) transitions were observed by dynamic mechanical analysis. The relationships between tensile properties and thermal transitions, the effect of the addition of CNT, and the structure evolution during the elongation at temperatures above the PAN alpha/alpha(c) transition were investigated. Understanding of the drawing behavior of PAN and PAN/CNT is important so the highest property carbon fibers can be processed from these fibers. (c) 2013 Elsevier Ltd. All rights reserved.