A survey of literature reveals that the use of Pitzer approach for modeling electrolyte in nonaqueous or in mixed solvent media is still very scarce. Moreover, only two research groups have used the exact and complete form of the more refined Pitzer-Simonson-Clegg (PSC) ion-interaction approach for the investigation of electrolyte in mixed solvent systems. The present investigation describes the results obtained by the use of Pitzer, PSC as well as an extended PSC ion-interaction approaches for modeling the non-ideal behavior of the ternary HCl + water + I propanol systems. These 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 performed over the HCl electrolyte molality ranging from 0.01 up to 4.5 mol kg(-1) in the ternary HCl + 1-propanol (x%) + water (100 - x%) system with different alcohol percent mass fractions (x% = 10, 20,30,40 and 50%), at 298.15 +/- 0.05 K. (C) 2009 Elsevier B.V. All rights reserved.