Aqueous monoethanolamine (MEA) is widely used for CO2 capture and has been demonstrated as an effective absorbent in many postcombustion capture plants. However, several disadvantages such as toxicity, high volatility, solvent degradation, and high energy consumption were reported in the practical applications. Aqueous amino acid salts, particularly potassium lysinate (LysK), are considered as attractive alternatives to MEA. A comparative study of absorbent characteristics of aqueous LysK (2.0 M and 2.5 M) and aqueous MEA (5.0 M) was conducted in this study. The absorption and cyclic capacities, absorption and desorption rate, solubility of CO2, and heat of absorption were measured using a stirred batch-type reactor and a CPA201 reaction calorimeter under similar postcombustion capture conditions. Thermal and oxidative degradation was also evaluated for aqueous 2.0 M LysK at 383 and 423 K under static N-2 and O-2 exposure conditions for 15 days. Samples were analyzed by total alkalinity and C-13 and H-1 NMR spectra to provide insight into the degradation products. The advantages of the comparable CO2 capture performance, high stability, and low solvent loss compared to the state-of-the-art solvent MEA, suggest LysK can be a potentially advantageous absorbent for industrial CO2 capture processes.