We report in this work, for the first time, the results obtained from both Pitzer, Pitzer-Simonson-Clegg (PSC) and an extended PSC ion-interaction approaches for modeling the non-ideal behavior of HCl electrolyte in the mixed ethanol + water solvent systems. In this context, a review of literature shows that the use of an exact and complete form of PSC ion-interaction approach for modeling electrolyte in mixed solvent systems was only limited to the works of two research groups. In this work, the modeling purposes were achieved based on the experimental potentiometric data of a galvanic cell containing a pH glass membrane and Ag/AgCl electrodes. The measurements were achieved over the HCl electrolyte molality ranging from 0.02 up to about 5 mol kg(-1) in mixed ethanol (x%) + water (100 - A) solvent with different solvent mass fractions percent (x% = 10%. 20%, 30%, 40% and 50%), at 298.15 +/- 0.05 K. (C) 2009 Elsevier B.V. All rights reserved.