A method for grafting polypropylene (PP) onto graphene oxide (GO) surfaces was successfully established by functionalizing GO with (3-aminopropyl)triethoxysilane (NH2-t-GO) and grafting maleic-anhydride-grafted PP (MAPP) on NH2-t-GO (MAPP-g-GO). The PP/GO nanocomposites were prepared by compounding MAPP-g-GO with virgin PP. The modulus, tensile strength, and elongation at break of the nanocomposite were improved by 48%, 37%, and 19%, respectively, by incorporating 0.6 wt% MAPP-g-GO (0.06 wt% GO). This improvement in the mechanical properties may be due to the good dispersion of GO in the PP matrix, which can be achieved via the excellent interactions between the grafted PP on GO and the matrix PP.