The multi-walled carbon nanotubes (MWCNTs)/polypropylene (PP) nanocomposites were fabricated by the melt mixing method. MWCNTs were chemically treated by immersing them in acidic solutions to ensure extensive dispersion in the surrounding matrix. From the Fourier transfer infrared spectroscopy (FTIR), Raman spectroscopy, thermogravimetric analyzer (TGA) and X-ray diffraction (XRD) tests, it can be observed that the MWCNTs has been successfully modified by acid solutions. Scanning electron microscopy (SEM) has shown that MWCNTs are distributed reasonably uniformly. It showed that the hardness of nanocomposites increased with increase in MWCNTs content. The tensile strength, tensile modulus and impact strength of nanocomposites increased with MWCNTs content to a maximum value at 3phr, and then decreased. The all mechanical properties of acid-modified MWCNTs reinforced PP nanocomposites were more outstanding than that of unmodified MWCNTs.