The solute-solvent interactions of some phenol derivatives were investigated potentiometrically in 0-60 % (v/v) ethanol-water mixtures. The acidity constants values were correlated with either macroscopic parameters such as molar fraction, permittivity and the solvating ability or microscopic parameters, such as the Kamlet-Taft solvatochromic parameters. Moreover, it is demonstrated that the pK (a) values in any ethanol-water mixtures are linearly related to the pK (a) values of the phenols in pure water. The slope and intercept parameters of the linear correlations are related with the mole fraction of ethanol. These equations permit accurate calculation of the pK (a) values of the studied phenols at any ethanol-water composition.