In the present work, the equilibrium solubility of carbon dioxide (CO2) in aqueous amine mixture solutions of 2-((2-aminoethyl)amino) ethanol (AEEA) and N-methyldiethanolamine (MDEA) is measured in the temperature range of 308.2 K to 368.2 K and the pressure range of 101 kPa to 4448 kPa. The (vapor + liquid) equilibrium of binary AEEA and water system is measured at constant pressure of 86.6 kPa. The dielectric constant of AEEA is also obtained experimentally in the temperature range of 293.2 K to 348.2 K. For thermodynamic modeling the electrolyte modified Peng-Robinson cubic plus association equation of state (emPR-CPA EoS) [A.T. Zoghi, F. Feyzi, M.R. Dehghani, Ind. Eng. Chem. Res. 51 (2012) 9875-9885] is applied and the solubility of CO2 in the aqueous mixture of AEEA and MDEA is obtained. In order to model the quaternary system, parameters of the emPR-CPA EoS are first adjusted for pure components. Then, the binary molecular interaction parameters for binary sub systems (CO2-Water, CO2-MDEA, CO2-AEEA, MDEA-Water, AEEA-Water) and the ionic interaction parameters for ternary sub systems (MDEA-CO2-Water) and (AEEA-CO2-Water) are optimized. By the emPR-CPA EoS the CO2 solubility is obtained in the ternary sub-systems (MDEA-CO2-Water) and (AEEA-CO2-Water) with average absolute percent deviations (AAD%) equal to 17.32 and 14.63, respectively. Finally, the equilibrium solubility of CO2 in aqueous mixture of AEEA + MDEA is obtained with AAD% = 24.3 and root mean square relative deviation percent (RMSD%) = 27.67. (C) 2013 Elsevier Ltd. All rights reserved.