CO2 absorbents were prepared from polyethylene glycol and the polyamidines having N,N'-disubstituted amidine structure in the main chain synthesized through acid-catalyzed melt polycondensation of orthoesters and alpha,omega-diamines. The homogeneous binary mixtures with the polyamidines captured CO2 much more efficiently under CO2 flow than the one with polyethyleneimine. Furthermore, we investigated the CO2 capture and release by the binary mixtures in terms of effects of the volatility and the structure of polyamidines, temperature, and polyethylene glycol. Taking into consideration the results thus obtained, we conducted CO2 capture/release cycles with the CO2 capture step at 40 A degrees C and with the CO2 releasing step at 80 A degrees C in an alternating manner, thereby demonstrating the repeatability of CO2 capture and release by the binary system of the polyamidine and polyethylene glycol.