A novel technique to modify the surface of calcium carbonate (CaCO3) nanoparticles, used as an antioxidant and reinforcing filler, by gallic acid is disclosed. The new properties of the modified CaCO3 could make it more useful and practical for the rubber industry. Thermal gravimetric (TGA), Fourier transform infrared spectroscopy, and transmission electron microscopy analyses showed that the gallic acid was bound onto the surface of CaCO3. The gallic acid modified CaCO3 exhibited a significant antioxidation property, as revealed by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) analysis. The mechanical properties of natural rubber vulcanizates filled with the gallic acid modified CaCO3 showed an enhanced reinforcement with increasing loading levels, and increased resistance to ozonolysis over that seen with the unmodified CaCO3 mixed with Irganox 1010 as the commercial antioxidant.