Oxidative and thermal degradation of alkanolamines for a promising CO2 capture technology of absorption might cause decrease in CO2 capture efficiency and formation of hazardous byproducts. In this study, characteristics of a representative absorbent of monoehtanolamine (MEA) were examined for a long term operation using a laboratory scale absorption system. An CO2 absorption system with ID 56 mm and absorption zone height 100 cm was developed for the characterization. Absorption solution of 30 wt% MEA was circulated at 100 mL/min to treat air with 15% CO2 and 1 ppm NO at 10 L/min. Temperatures of absorber and stripper were maintained at 40℃ and 120℃, respectively. For the course of 5 weeks continuous operation, MEA concentration was decreased approximately by 70% and CO2 removal efficiency was dropped from 95% to 65%. Ionic byproducts of NH4 +, NO2 -, and NO3 - were accumulated up to 48 g/mL, 0.2 g/mL, and 1.5 g/mL, respectively, tracking the variation of MEA concentration. Formation of various organic byproducts were also observed.