Abstract: PP/graphene nanoplatelet (GNP) nanocomposites were prepared by using five different type of GNP fillers through a melt blending methods, and effects of size and content of GNP on electrical and thermal conductivity of nanocomposites were investigated. The results indicated that, at the same thickness of GNP, GNP with larger diameters could provide a greater contact area between the layers, thus improving the electrical and thermal conductivity of the nanocomposites. Moreover, at the same diameter of GNP, the thinner thickness resulted in a better dispersion of GNP in the matrix, and the nanocomposites achieved an improvement in electrical and thermal conductivity accordingly. It was also found that the effects of GNP content on the electrical and thermal conductivity were different for the samples of PG-100, PG-030 and PG-G5. PG-030 could easily form a conductive network at the lowest percolation threshold, and however, PG-G5 exhibited the highest electrical conductivity and thermal conductivity at a high content of GNP.