Graphene is a nanofiller with outstanding mechanical, electrical, and gas barrier properties because it is considered a carbon nanofiller which has a two dimensional structure with a one-atom-thick planar sheet of sp2 bonded carbon atoms that are densely packed in a honeycomb crystal lattice. Graphene-based polymer composites have attracted attention among the various applications of graphene because of their extraordinary electrical, mechanical, thermal, and gas barrier properties, which can be achieved using very low graphene loadings. However, the performance of graphene-based polymer composites is limited by the problem of graphene’s low dispersibility in polymer matrices, and particularly in non-polar polymers. This low dispersibility occurs, because graphene tends to aggregate due to its strong $\pi - \pi$ and van der Waals interactions. In this thesis we prepared and characterized poly(propylene)/graphene nanoplatelet (PP)/(GNP) nanocomposites, using PP-grafted thermally reduced graphene oxide (TRGO) as a compatibilizer to enhance mechanical , electrical, gas barrier and melt strength properties. In chapter 2, we optimized the synthesis of the compatibilizers by controlling the temperature of the reduction of graphene oxide. And chapter 3, we synthesized the PP-g-TRGO for compatibilizer of PP/GNP nanocomposites. In chapter 4, we fabricated the PP/PP-g-TRGO/GNP nanocomposites by and characterized the crystallinity and mechanical, electrical, gas barrier and melt strength properties by melt blending method. The crystallinity, mechanical, electrical, gas barrier and melt strength properties of PP/GNP nanocomposites were enhanced by the presence of only 0.1 wt.% PP-g-TRGO compatibilizer.