Cubic plus association equation of state was applied for the first time to calculate various thermodynamic properties such as activity coefficient, solubility, density, and vapor pressure of aqueous solution of amino acids. Pure compound parameters of CPA EOS were fitted to the activity coefficient of amino acids in aqueous solution. In order to calculate the monomer fractions of amino acids and water in a binary solution of these molecules, a novel 3rd degree linear equation was proposed. The model also has been used to correlate the solubility of amino acids in different temperatures, and the values of Delta h and Delta s were obtained through the calculation of solubility in water. In addition, a group contribution method was applied to estimate the critical temperature. CPA in contrast with the other equation of states (e.g. SAFT EOS) that previously used to correlate thermodynamic properties of amino acids has the advantage of simplicity. Moreover, the results showed good agreement with the experimental data. (C) 2016 Elsevier B.V. All rights reserved.