The dissociation enthalpies of o-, m-, p-amino benzoic acid in water-ethanol mixtures ranging from pure water up to 0.477 molar fraction of ethanol have been determined at 298.15 K by the method of mixing-flowing microcalorimetry. Combined with the available values of Gibbs free energy reported in the literature, the corresponding values of dissociation entropy have been calculated. The enthalpic and entropic effects arising from solvent and substituent have been discussed in terms of solute-solvent interaction and tautomeric equilibrium.