With the increasing demand for higher performance and progressive miniaturization of electronic packages, power densities and the attendant thermal dissipation requirements are expected to escalate. One of the important strategies to ensure reliable operation at the device and die (chip) levels is the use of Thermal Interface Materials (TIMs) to reduce the thermal resistance between the chip and the heat sink. In this study, we have carried out an experimental investigation to characterize thermal conductance of TIMs composed of commercially available graphene (c-rGO), graphene nanoplatlets (GNPs) of different lateral sizes (5, 15 and 25 μm), and our in-house produced thermally reduced graphene oxide at 600°C (T-rGO-600). These additives were loaded in a silicone rubber matrix where their loading fraction was fixed at 2% by weight. Thermal conductance of the resulting TIMs was determined by measuring heat flow, in steady state, through a TIM sandwiched between two metal blocks. The thermal conductance values representing the combined resistance of the composite material and the contact resistances between the TIM and the metal blocks were measured at different heat flux levels across the TIM. The results show that the thermal conductance values were independent of the heat load across the TIM as well as the TIM temperature. Further, a detailed investigation of the surface functionality and structural properties has revealed that the in-house produced T-rGO-600 has superior thermal conductance when compared to the above-mentioned carbonaceous nanomaterials, which are considered as potential candidates for enhancing thermal performance of TIMs. The data demonstrates that this result is attributable to the formation of the surface functional groups and the associated morphological changes during the reduction of graphene oxide to the T-rGO-600. Among the different GNPs tested, the GNP-15 exhibited superior thermal performance compared to the GNP-5 and GNP-25 samples.