Current highly integrated devices require heat interface materials with excellent heat conductivity. A simple approach was employed to synthesize thermally conductive and outstanding thermal stability nanocomposite. Calcium carbonate nanoparticles (nano CaCO3) reinforced with reduced graphene oxide (rGO) nanoparticles (rGO/CaCO3) are synthesized using a novel process, and the effect of rGO in CaCO3 structure is examined by Field Emission Scanning Electron Microscope, X-ray diffraction, TGA-DTA, and thermal conductivity. The experimental results show that adding rGO resulted in higher crystallinity and thermal stability. As the wt.% of rGO increases from 1 to 5%, the crystallite size was suppressed by 21.06%, 27.39%, 32.48%, 41.5%, and 45.30%, respectively, compared to the pure nano-CaCO3. Additionally, rGO enhances the thermal conductivity by 35.31% and thermal diffusivity to 1.834 mm2/s by adding 5% rGO.