The solubility of 4-ethyl-1-phenyl-1,3-octadione in pure water, (NH4)(2)SO4, NH3 (aq), and (NH4)(2)SO4-NH3-H2O solutions was measured by means of isothermal solution method at 298.15 K. The investigated total ammonia concentration ranges of NH3, (NH4)(2)SO4, and (NH4)(2)SO4-NH3-H2O system were up to 1.8053 +/- 3.0135 mol.L-1, 3.0135 mol.kg(-1), and 6.4 mol.kg(-1), respectively. The experimental results indicate that the solubility of 4-ethyl-1-phenyl-1,3-octadione in NH3 and (NH4)(2)SO4-NH3-H2O solutions increases with the increase of total ammonia concentration. In contrast, its solubility in (NH4)(2)SO4 solution decreases with the increase of the ammonium sulfate concentration. The Pitzer model was adopted to correlate the dependency of the solubility with the activity coefficients. The parameters obtained by the least-squares method can explain the salting effect phenomenon and can be used to calculate and predict the activity coefficients of 4-ethyl-1-phenyl-1,3-octadione in ammoniacal solutions by the Pitzer model.