A series of polyethylenimine (PEI)-linked microporous organic polymers were obtained using glycidyl methacrylate-polyethylenimine monomer (GMA-PEI) and different cross-linking agents. Because of well-defined micropores and CO2-philic plentiful secondary amines, porous organic polymers (POPs) demonstrate high CO2 uptake and excellent selectivity over other permanent gases, such as CH4 and N-2. The adsorption capacity of POPs reaches 92 mg g(-1) at 273 K and 1 bar, which is higher than that of recently reported polymers supported on various porous materials such as MCM-41 (33 mg g(-1)), alumina (50 mg g(-1)), and SBA-15 (60 mg g(-1)) under the analogous conditions. The high CO2/N-2 and CO2/CH4 selectivity is observed and reaches 308 and 39, respectively. It is noteworthy that POPs can be entirely regenerated under mild conditions and no loss in activity is detected after four cycles. Notably, no side product is obtained during the fabrication of POPs. Thus, good adsorption capacity, high selectivity, and energy-saving regeneration of POPs make their use in selective CO2 capture from flue gas and natural gas promising.