The present paper investigates the various CO2 absorption behaviors in relatively highly concentrated monoethanolamine (MEA) solvent systems, containing 1-5 M MEA, based on the experimental results as well as the ionic conductivities of carbamic acid (RNH3+) and carbamate (RNHCOO-) reported in our previous study. Initial measured electrical conductivity (ECm) and effective RNH3+ concentration of the solvents decreased as the MEA concentration increased. The ratio of RNHCOO- hydrolyzed to free amine was also reduced according to MEA concentration, thus causing a decrease in the ratio of total CO2 absorbed to MEA concentration as the MEA concentration increased. The activity coefficient of the solvent also decreased with increase of the MEA concentration. These phenomena may be primarily ascribed to the lack of a sufficient amount of water molecules to surround and block the interaction between the two separated ions in the system, RNH3+ and RNHCOO-, as compared to low concentration solvent systems. Finally, the amount of CO2 absorbed in the system was almost proportional to ECm in each solvent, thus an equation for general estimation of the amount of CO2 absorbed by measurement of the ECm variation in a given highly concentrated MEA solvent was derived.