Oxidative degradation characteristics of silica‐supported amine sorbents with varying amounts of tetraethylenepentamine (TEPA) and polyethylene glycol (PEG; P₂₀₀ or P₆₀₀ represents PEG with molecular weights of 200 or 600) have been studied by IR and NMR spectroscopy. Thermal treatment of the sorbents and liquid TEPA at 100 °C for 12 h changed their color from white to yellow. The CO₂ capture capacity of the TEPA/SiO₂ sorbents (i.e., SiO₂‐supported TEPA with a TEPA/SiO₂ ratio of 25:75) decreased by more than 60 %. IR and NMR spectroscopy studies showed that the yellow color of the degraded sorbents resulted from the formation of imide species. The imide species, consisting of NH associated with two CO functional groups, were produced from the oxidation of methylene groups in TEPA. Imide species on the degraded sorbent are not capable of binding CO₂ due to its weak basicity. The addition of P₂₀₀ and P₆₀₀ to the supported amine sorbents improved both their CO₂ capture capacities and oxidative degradation resistance. IR spectroscopy results also showed that TEPA was immobilized on the SiO₂ surface through hydrogen bonding between amine groups and the silanol groups of SiO₂. The OH groups of PEG interact with NH₂/NH of TEPA through hydrogen bonding. Hydrogen bonds disperse TEPA on SiO₂ and block O₂ from accessing TEPA for oxidation. Oxidative degradation resistance and CO₂ capture capacity of the supported amine sorbents can be optimized through adjusting the ratio of hydroxyl to amine groups in the TEPA/PEG mixture.