The phase-forming salts and their corresponding phase-forming abilities for 1-butyl-3-methylimidazolium-tetrafluoroborate ([Bmim]BF4)-based aqueous two-phase were discussed. The phase-forming abilities of (NH4)(2)SO4 and Na2CO3 for [Bimim]BF4-based aqueous two-phase were compared and discussed. Phase diagrams were experimentally determined for aqueous two-phase systems containing [Bmim]BF4 and (NH4)(2)SO4 at T=298.15, 308.15, and 318.15 K. The Merchuk equation was used to correlate the binodal data of these systems. Simultaneously, the effect of temperature on the phase-forming ability in the investigated system has also been studied on the basis of a salting-out coefficient obtained from fitting the tie-line data to a Setschenow-type equation for each temperature. (C) 2010 Elsevier B.V. All rights reserved.