Tetraethylenepentamine (TEPA), consisting mainly of primary and secondary amines, exhibits a high CO2 sorption capacity; however, its poor thermal stability hampers process for CO2 capture. Here, a facile functionalization of practical utilization in the temperature swing adsorption TEPA with 1,2-epoxybutane (EB) substantially enhanced its thermal stability as well as the CO2 adsorption kinetics. Our careful analysis on the liquid-state C-13 NMR disclosed the amine state distribution of EB-functionalized TEPA (EB-TEPA). Although the increase in tertiary amine portion induced by EB-functionalization reduced CO2 sorption capacity, the 0.64EB-TEPA (i.e., TEPA functionalized with EB with a TEPA/EB molar ratio of 1:3)/SiO2 showed an excellent long-term stability over the 10 consecutive cycles of adsorption/desorption processes with a CO2 swing capacity of 2.0 mmol CO2 g(-1) under dry CO2/N-2 (15/85 mol/mol) feed conditions. Also, the first-principles calculation identified the configuration of modified TEPA molecules with XRD measurements, supporting an easy access of CO2 into amine moieties of our modified TEPA molecules.