Acid orange 7 acidity constants were determined in water, in sodium chloride, and in sodium sulfate solutions, from spectrophotometric measurements, within the temperature range (278.15 to 333.15) K. The salt molalities were lower than (2 and 0.7) mol.kg(-1) for sodium chloride and sodium sulfate solutions, respectively. Stoichiometric acidity constants were determined in those ionic media to assess the influence of those two salts on the acid-base equilibrium. Deviations from ideal behavior were estimated by the evaluation of the activity coefficients of the ions that take part in the chemical equilibria by means of the Debye-Huckel theory. Expanded Debye-Huckel equations showed a good fit to the experimental data within the considered temperature range. The results also indicate the formation of dye aggregates at high ionic strength which is more evident as the temperature decreases.