Amine-functionalized silica adsorbents are promising materials for CO2 capture since they demonstrate good selectivity to CO2 at low partial pressure, considerable adsorption capacity, and low energy consumption. Exposure of CO2 adsorbents to acidic gases in flue gases including SOx and NOx would have a detrimental effect on the capture process. In this study, adsorbents with primary (1NS-P) and secondary (1NS-S) amine and polyethyleneimine (PEI) were synthesized by impregnation and then exposed to acidic gases to investigate the effects of exposure time, temperature, and concentration of SO2 and NO2 on the degradation of supported amine adsorbents. It was found out that nitro groups, NH2-SO2 (NO2) complexes, and amide structures were formed at both high and low temperatures. PEI, which is one of the most widely used amines for CO2 adsorbents, was also evaluated in the presence of acidic gases to determine its resistance and stability using TG and in-situ IR analysis. The adsorbents showed a steady decrease in CO2 adsorption capacity when exposed to SO2 and NO2 concentrations above 20 ppm. The concentration and exposure temperature of acidic gases were the most influential factors for CO2 adsorption capacity of amine-supported adsorbent.