Systemic investigation of the influence of the plain and functionalized carbon nanotube (CNT) contents on the ultradrawing properties of ultrahigh molecular weight polyethylene/carbon nanotubes (UHMWPE/CNTs, FCy) and UHMWPE/functionalized CNTs (FCfx-y) as-prepared fibers are reported. In a way similar to those found for the orientation factor values, the achievable draw ratios (D-ra) of the FCy and FCfx-y as-prepared fibers approached a maximum value as their CNT and/or functionalized CNT contents reached their corresponding optimum values. The maximum D-ra values obtained for FCfx-0.001 as-prepared fiber specimens prepared at varying maleic anhydride grafted polyethylene (PE-g-MAH)/modified CNTs weight ratios were significantly higher that of the FC0.0015 as-prepared fiber specimen prepared at the optimum plain CNT content. Tensile property analysis further suggested that excellent orientation and tensile properties of the drawn FCy and FCfx-y fibers can be obtained by ultradrawing the fibers prepared at their optimum plain CNT and/or functionalized CNT contents. To understand the interesting orientation, ultradrawing and tensile properties of FCy and FCfx-y fiber specimens, FTIR, specific surface area, and SEM morphology analysis of the plain and functionalized CNTs were performed in this study. POLYM. ENG. SCI., 51:687-696, 2011. (C) 2010 Society of Plastics Engineers