The thermodynamic properties of (HCl (m(A)) + NaCl (m(B))-tert-C4H9OH + H2O) system were studied by means of e.m.f. measurements in the cell without liquid junction at constant total ionic strength I - 1.00 mol (.) kg(-1) from 278.15 K to 318.15 K, The standard electrode potential of Ag-AgCl and activity coefficient of HCl in the mixed solvents have been determined. The results show that the activity coefficient of HCl in HCl-NaCl solution still obeys Harried's Rule and the logarithm of HCl activity coefficient, 1g gamma(A), is a linear function reciprocal of temperature at constant composition of the mixture. The standard transfer Gibbs free energy of HCl was calculated. (C) 2004 Elsevier Ltd. All rights reserved.