New experimental data for equilibrium solubility of carbon dioxide in aqueous solutions of N-methyldiethanolamine (MDEA) and piperazine (PZ) are reported for temperature range of 363-423 K and pressure range of 26.3-204.3 kPa. The measured data in combination with the data collected from literature are used to modify Deshmukh-Mather model for prediction of the solubility of carbon dioxide in MDEA + PZ solutions. In this model, a modified extended Debye-Huckel expression for electrolyte solutions is used for the calculation of activity coefficients. More than 300 data points in a wide range of temperatures, pressures and concentrations are used to optimize the interaction parameters for the studied system. Genetic Algorithm minimization technique is used for this optimization process. The gas-phase fugacity coefficients are also included and are calculated using Peng-Robinson equation of state. The predictions of the proposed model are compared with the experimental data reported by Liu et al. The results show a very good agreement between experimental data and model predictions. (C) 2013 Elsevier B.V. All rights reserved.