ABSTRACT Rubber composites were synthesized by natural rubber filled with cerium oxide with different particle diameters. The dispersion morphology of cerium oxide in rubber matrix and the mechanical properties of composites were studied, and the contrast experiment of reinforcing rubber with cerium oxide was performed. The results showed that the small particles of cerium oxide had better disparity than the large particles of cerium oxide in NR. The mechanical properties of rubber filled with small particles of cerium oxide were better than those of rubber filled with large particles of cerium oxide. The crystalline rubber was measured by X-ray diffraction, which indicated that the CeO2 accelerated crystallization capacity and confined the rubber chain movement. The tensile strength of rubber was increased by this confinement.