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CO2 emission is generally regarded as the major contributor to global climate change, and polyethylenimine (PEI)-based CO2 adsorbents are promising materials for the capture of low concentration CO2. This paper deals with the deactivation kinetics of PEI-based CO2 adsorbents used for the capture of low concentration CO2. EA and TG analyses demonstrated that thermal degradation and O-2-induced deactivation of the adsorbents occurred simultaneously under air exposure conditions. It was found by N-2 exposure experiments at the temperature of 50-80 degrees C that the thermal degradation of PEI-based adsorbents followed a first-order reaction model with an activation energy of 80.98 kJ/mol and a pre-exponential factor of 6.055 x 10(8) (h(-1)). The parallel reaction model was employed to distinguish the O-2-induced deactivation from the thermal degradation of the adsorbents through air exposure experiments within 50-80 degrees C. The O-2-induced deactivation exhibited a second-order reaction with an activation energy of 74.47 kJ/mol and a pre-exponential factor of 6.321 x 10(6)(%(-1).h(-1)). The results of simulating the overall deactivation of the adsorbents by the parallel reaction kinetic model were well consistent with those of the experiments, proving that the parallel reaction model was feasible for the description of the deactivation of PEI-based adsorbents.