Aqueous potassium salt solutions of L-alanine and L-proline were investigated as carbon dioxide (CO2) absorbents. The CO2 absorption capacities and absorption heats (-Delta H-abs) of the aqueous amino acid salts were measured in a semi-batch absorption system and differential reaction calorimeter (DRC). The solution experiments tested concentrations of 2.5 M and were carried out at 298 and 313 K. The C-13 and H-1 nuclear magnetic resonance (NMR) spectra were used to identify the species distributions in the CO2-loaded absorbents. The absorption properties were compared to those of the commercial monoethanolamine (MEA) absorbent, revealing that the CO2 loading capacity was higher than that of MEA (0.68 mol of CO2/mol of solute for the potassium salt of L-alanine > 0.5 mol of CO2/mol of solute for MEA). The absorption heat was lower than that of MEA at 298 K (53.26 kJ/mol of CO2 for the potassium salt of L-alanine < 81.77 kJ/mol of CO2 for MEA).