Electromagnetic wave absorbing materials have received increasing attention in electrical and communication industries. Electrically conductive nanocomposites based on graphite, carbon black, carbon nanotube and etc, have been considered to exhibit high potential in shielding the electromagnetic waves. In the present work, various electrically conductive nanocomposites based on RTV Silicon rubber and a hybrid nano system comprising conductive carbon black and graphite nanosheets (GNS) were fabricated. Effectiveness of this conductive hybrid in attenuation of electromagnetic wave energy by the corresponding nanocomposite has been investigated. Nanocomposites generated by GNS/CB showed lower percolation threshold with enhanced conductivity compared with GNP sample. Dynamic Mechanical Thermal analysis (DMTA) was performed to find out correlation between mechanical damping behaviors with electromagnetic wave absorbing capacity. Nanocomposite derived by GNS/CB hybrid revealed a double tanδ peaks in tanδ-frequency plot, indicating the presence of two types of physical formed networks by the CB and GNS particles in the form of segregated solid phases in the matrix of RTVSR. Melt rheomechanical spectrometry (RMS) showed higher tendency of CB particle to structured than graphite nanosheets. All crosslinked RTV samples filled by CB/GNP hybrid exhibited synergistic potential in attenuating the electromagnetic wave energy within the frequency range of 8-12 Ghz. The nanocomposite originated by 12wt% of GNP/CB revealed more absorption than sample based on 12wt% GNS.