Polypropylene (PP)/ethylene propylene diene monomer (EPDM)/graphene nanosheets (GNs) were compounded by a two-step melt mixing process via an internal mixer (brabender plasticorder). The effect of GNs, graphene oxide (GOSs) and graphene oxide functionalized with PP chains (PP-g-GOSs) on various blend properties were investigated. Wide X-ray diffraction (WAXD) patterns and transmission electron microscopy (TEM) images of the prepared nanocomposites revealed that the nanofillers were mostly dispersed into the PP phase and the dispersion state of GNs was improved with functionalization of graphene. SEM photomicrographs indicated that rubber droplets were distributed in the PP phase and a reduction of the dispersed EPDM droplet size was observed most likely due to increase in the viscosity of the PP-phase during melt mixing. The effects of nanofillers on thermal, mechanical and rheological properties were reported, and the obtained results were discussed in terms of morphology, state of dispersion and distribution of the nanofillers within the PP matrix. As for the mechanical properties, an improvement of 56% in tensile modulus and 48% in tensile strength, while 72% reduction in elongation at break was observed. The DMTA results revealed that the nanocomposites based on PP-g-GOSs had lower damping behavior and the intensity of the loss factor decreased by increasing the GNs content. These results indicate the presence of a strong interfacial interaction between the nanoplatelets and the polymer matrix.