The properties of polypropylene (PP)/multi-walled carbon nanotubes (MWNTs) composite were examined. MWNTs were wrapped with polypropylene-graft-maleic anhydride (PP-g-MA) followed by functionalization with hydrogen peroxide ($H_2O_2$) for good dispersion in a PP matrix. The $H_2O_2$-treated MWNTs were characterized by Raman spectroscopy (RAMAN) and Elemental analysis (EA). These results suggest that hydroxyl groups were introduced to the nanotube surface. The homogeneously dispersed PP/MWNT nanocomposites were prepared by melt mixing using a twin-screw extruder. The SEM images of the neat MWNTs and functionalized MWNTs showed that the functionalized MWNTs had been dispersed well in the matrix whereas the neat MWNTs (N-MWNTs) aggregated. Thermal analysis and the stress-strain data showed that the well dispersed MWNTs in the PP matrix greatly enhanced the mechanical and thermal properties of polypropylene.