Activity oefficients and solubilities of L-Alanine in aqueous solutions containing each of four electrolytes (NaCl, KCl, NaNO3 and KNO3) were measured at 298.15 K. The measurements of activity coefficients were carried out in the electrochemical cell coupled with two ion-selective electrodes(cation and anion), and the solubilities were measured by the gravimetric analysis of saturated solutions in equilibrium with the solid phase of L-alanine. To model the activity coefficients and solubilities of amino acid in the amino acid/electrolyte aqueous solutions, thermodynamic relations of the residual Helmholtz free energy in the amino acid/electrolyte aqueous solutions were developed based on the perturbed-chain statistical associating fluid theory(PC-SAFT) combined with the primitive mean spherical approximation(primitive-MSA). In the present model, it is assumed that the zwitterions of L-alanine are associated with each other and cross-associated with water molecules, and also cross-associated with the cation and anion dissociated from an electrolyte(inorganic salt). The activity coefficients and solubilities of L-Alanine calculated from the theoretical model proposed in this work are found to be well agreeable with experimental data.