Abstract: Well-aligned, long fibers composed of multi-walled carbon nanotubes (MWNTs) and polypropylene (PP) were fabricated by a conventional melt spinning technique. Scanning electron microscope (SEM) observations of the morphology revealed that both the alignment and dispersion of MWNTs in the matrix were improved. Mechanical properties of the composite fibers were studied by tensile testing and Weibull distribution, and it was found that their tensile strength was increased with addition of the carbon nanotubes. The maximum tensile strength of 61MPa was achieved at 3w/% MWNT addition, 120% more than that of the pure PP fibers. Moreover, a unique tensile rupture characteristic was found by SEM observations, which explained the critical phenomenon that the MWNT addition affects the tensile property of the MWNT composite fibers.