Since the development of amine-functionalized adsorbent is critical for its large-scale implementation, an investigation on the stability in realistic process condition is significantly important. The amine-functionalized CO2 adsorbents were prepared via impregnation of primary amine (1NS-P/SiO2), secondary amine (1NS-S/SiO2) and diamines (2NS/SiO2) into a silica support. The degradation products that could have caused the deactivation of the adsorbents are determined and quantified by in-situ FT-IR measurement and deconvoluted FT-IR spectra. The adsorbents were evaluated for their stability in multiple temperature swing adsorption (TSA) cycles and long-time CO2 or air exposure at elevated temperature. It revealed that the degradation of adsorbents and its rate depended on the amine structure and gas conditions and that two main degradation species were urea and amide. Primary amine was more prone to CO2-induced degradation than secondary amine. Secondary amine was less stable than primary amine for O-2-induced degradation. Diamine showed both CO2- and O-2-induced degradations. To assess which has a more detrimental effect on the stability of the adsorbents between CO2 and O-2 gases, the effect of long-time exposure of the adsorbents in pure CO2 or air was determined at 150 degrees C using both TG and in-situ FT-IR measurement. The long-time exposure of 1NS-P/SiO2 to CO2 caused about 50% loss in CO2 uptake with the faster accumulation of linear urea. The long-time exposure to air caused just about 13% loss in CO2 uptake with the slower accumulation of amide. 1NS-S/SiO2 showed better stability for CO2 than 1NS-P/SiO2 without any decrease in capacity and without any changes in its spectra. 2NS/SiO2 showed that urea formed faster than amide. It was degraded more in air than in CO2 with about 92% and 51% loss of CO2 uptake, respectively. It can be inferred from the results that O-2-induced degradation is more detrimental than CO2-induced degradation.