Absorption in aqueous alkanolamine solutions is frequently used for CO2 separation from various gas streams. In the present study, a reaction calorimeter was used to measure solubilities and enthalpies of absorption Of CO2 in aqueous solutions of N-methyldiethanolamine in the temperature range of (293.15 to 333.15) K and amine concentration range of (10 to 40) mass%. Experiments were performed at CO2 partial pressures of (0.1 and 0.3) MPa. The experimental equipment and procedure were described with the emphasis on complexity originating from the difficulty of interpreting the chemical absorption data and measuring the enthalpy of absorption. The enthalpy of absorption was found to be independent of pressure and linearly dependent upon the temperature and amine concentration.