AbstractNovel rubber antioxidants, cysteine lanthanum and cysteine cerium, were applied in natural rubber composites. The anti-aging behavior of the composites with rare-earth complexes was systematically investigated via mechanical properties retention after aging, Fourier transform infrared spectroscopy-attenuated total reflection, thermo-oxidative stability and thermo-oxidative degradation kinetics. The results showed that rare-earth complexes could improve the mechanical properties of composites, decrease the formation of thermo-oxidative products and increase activation energy of the thermo-oxidative degradation. Compared with commercial antioxidant N-isopropyl-N '-phenyl-p-phenylenediamine, the vulcanizates with cysteine lanthanum performed better resistance to thermal oxidation aging. The outstanding anti-aging behavior of rare-earth complexes was attributed to not only the anti-oxidative effect between amino and sulfhydryl groups, but the trapping effect of rare-earth ions on free radicals.