Polypropylene fibers containing varying amounts of multi walled carbon nanotube (MWCNT) have been spun using a conventional melt spinning and drawing apparatus. Changes in morphology and crystalline structure of composite fibers induced by addition of MWCNT were studied by small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS), Fourier transform infrared spectroscopy (FTIR) and birefringence measurements. The results of SAXS experiments showed an increase in lamellar thickness, long period and crystallinity of the composite fibers in comparison to pure polypropylene fibers. Molecular orientation and helical content of the fibers were increased due to the addition of MWCNT to the polypropylene matrix. WAXS results, being in agreement with the SAXS results, also showed an increase in crystallinity of the composite fibers due to the increase in MWCNT content. This is probably because of nucleating effect of nanotubes in the fiber matrix, causing more crystallization and orientation of molecules to take place around them.