Solubility data of CO2 in aqueous Mixtures of 2-amino-2-hydroxymethyl-1,3-propanediol (AHPD) and piperazine (Pz) were measured over a range of temperature from 288.15 to 333.15 K and for total amine concentrations up to 3.1 kmol.m(-3). The CO2 partial pressure was kept within 0.21-2 637 kPa using a vapor-liquid equilibrium (VLE) apparatus based on a static-analytic method. The solubility of N2O in the Pz-AHPD aqueous Solutions was also performed in order to determine, with the N2O analogy, the Henry's law constant of CO2 in these Solutions. The experimental data for the tertiary system AHPD-CO2-H2O were correlated using a modified Pitzer's thermodynamic model for the activity coefficients combined with the virial equation of state for representing the fugacity coefficients. The solubility of carbon dioxide in aqueous solutions of mixed amine (Pz + AHPD) was predicted by supposing that the parameters characterizing the single amine systems are essential for describing the quaternary system behavior.