Abstract Aqueous MDEA is the most commonly used solvent for H 2 S removal from natural gas. A reliable thermodynamic model is required for the proper design of natural gas sweetening processes. In this study, a rigorous thermodynamic model is developed to represent properties of the H 2 S–MDEA–H 2 O ternary system. The Extended UNIQUAC model is used to represent the system behavior. The model is created based on models for the constituent binary subsystems. The developed model provides accurate representation of VLE and heat of absorption for the studied system and subsystem in the temperature range of 0–180 °C, H 2 S partial pressure of 0.0033–8329.71 kPa, MDEA mass% of 0–50 and loading range of 0–2.17.