This article reports a study of the preparation of nanosilica-immobilized antioxidant (SiO2-APTMS-AO) and the thermal oxidative stability of low density polyethylene (LDPE) nanocomposites containing SiO2-APTMS-AO. SiO2-APTMS-AO was prepared based on the fumed nanosilica which was firstly modified with an aminosilane coupling agent and then reacted with 3,5-Di-tert-butyl-4-hydroxybenzoic acyl chloride. Infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis measurements confirmed that the antioxidant group was chemically immobilized onto nanosilica. LDPE/silica nanocomposites were prepared by melt mixing and then pressed into different films. The thermal oxidative stability of the nanocomposites was evaluated by thermogravimetric analysis in air atmosphere, oxidation induction time (OIT) and long-term accelerated thermal aging. The results showed that the SiO2-APTMS-AO can significant improve the thermal oxidative stability of LDPE nanocomposite. Because SiO2-APTMS-AO is based on inorganic nano-filler, in comparison to organic antioxidants, it might have advantages in thermal stability and migration stability during processing and application. (C) 2016 Elsevier Ltd. All rights reserved.