We report a novel method to improve the anti-thermal-deformation performance of an ethylene–octene copolymer (POE) using vinyl functionalized silica nanoparticles (M-SiO 2 ) as a sensitizer to enhance radiation-induced crosslinking. The M-SiO 2 nanoparticles were prepared by coupling commercially available silica nanoparticles with KH570 (γ-methacryloxypropyl-trimethoxysilane, γ-MPS) and were blended with POE by melt blending. Then, the mixture was irradiated with γ-rays under a nitrogen atmosphere to form the crosslinked POE/M-SiO 2 nanocomposite. The novel nanocomposites were characterized, and the results showed that the gel fraction was proportional to the content of M-SiO 2 in the loading range studied in this work. When the content of M-SiO 2 was 10wt%, the gel fraction of POE was increased by approximately 50%, and the softening temperature (T 0.5D ) increased from 104.4°C to 224.6°C after a 120kGy dose of radiation. The tensile strength of the POE/M-SiO 2 -10 nanocomposite was better than that of the neat POE copolymer irradiated with an absorption dose up to 100kGy. In contrast, the elongation of the POE/M-SiO 2 -10 nanocomposite was lower than that of the neat POE irradiated under the same conditions, due to the increased degree of crosslinking by radiation. These results clearly demonstrated that the use of M-SiO 2 as an irradiation sensitizer effectively enhanced the radiation-induced crosslinking of POE.