The densities of an aqueous solution of pure hydroxylamine sulfate at T = (283.15, 288.15, 293.15, 298.15, 303.15, 308.15, and 313.15) K and a solution of hydroxylamine sulfate containing ammonium sulfate at T = (293.15, 298.15, 303.15, 308.15, and 313.15) K have been determined over a wide range of concentrations. The viscosities of binary and ternary mixtures of these compounds at T = (298.15, 303.15, and 308.15) K are also presented. The Masson-type equation and extended Jones-Dole equation in terms of ionic strength are used to correlate the. density and viscosity, respectively, of aqueous solutions of hydroxylamine sulfate. The ideal mixing rule of Young has been successfully applied to predict the ternary densities and viscosities of aqueous hydroxylamine sulfate + ammonium sulfate based on relevant binary solution properties.