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, FC y ) and UHMWPE/functionalized CNTs (FC fx-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 FC y and FC fx-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 FC fx-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 FC 0.0015 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 FC y and FC fx-y fibers can be obtained by ultradraw-ing the fibers prepared at their optimum plain CNT and/or functionalized CNT contents. To understand the interesting orientation, ultradrawing and tensile properties of FC y and FC fx-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. ª FIG. 6. Tensile strength and modulus values of FC 0 , FC 0.0005 , FC 0.0001 , FC 0.0015 , FC 0.002 , FC f1-0.0005 , FC f1-0.001 , FC f1-0.0015 , FC f1-0.002 , FC f2-0.0005 , FC f2-0.001 , FC f2-0.0015 , FC f2-0.002 , FC f3-0.0005 , FC f3-0.001 , FC f3-0.0015 , FC f3-0.002 , FC f4-0.0005 , FC f4-0.001 , FC f4-0.0015 and FC f4-0.002 fiber specimens with varying draw ratios.