Crosslinked or vulcanized nanocomposites based on ethylene-propylene-diene-monomer rubber (EPDM) and electrically conductive nanographite synergized with ferromagnetic NiFe2O4 nanofiller have been fabricated via masterbach melt mixing in the presence of the maleated EPDM as interfacial compatibilizer, followed by hot crosslinking process. The role of interfacial compatibilization, and EPDM mooney viscosity and melt elasticity upon developed microstructure and conductivity percolation threshold as well as electromagnetic wave attenuation have been studied. AFM, FE-SEM, XRD, TEM and melt linear viscoelastic behavior were employed to characterize the internal microstructure of the prepared samples. Nancomposites based on nanographite and nano NiFe2O4 exhibited lower insulating to conduction transition threshold (ϕf=2) than counterpart samples originated by only nanographite (ϕf=3) together with higher potential in attenuation of the electromagnetic wave (X-band frequency) as a result of magnetic enhanced polarizability of the nanocomposites. However crosslink density of the nanocomposite vulcanizate showed to play significant role in controlling the conductivity threshold. Increasing the mooney viscosity and melt elasticity of the used EPDM rubber resulted in increase of percolation threshold and lower electrical conductivity at various weight of the graphite/NiFe2O4 nanosystem which is consisted with larger interparticle distances measured between nanoparticles. Electromagnetic wave attenuation was found also to be affected by the degree of the nanocomposites crosslinking, as the nanoparticles are forced to aggregate by increasing the crosslink density, resulting in enhanced conductivity and wave energy dissipation. Keywords: Electromagnetic Interference Shielding, Nanocomposites, Ethylene Propylene Diene Monomer (EPDM), Expanded Graphite (EG), Nano NiFe2O4