The phase diagrams and liquid + liquid equilibrium (LLE) data of the 1-butyl-3-methylimidazolium tetrafluoroborate {([Bmim]BF4) + Manganese sulfate (MnSO4) + water} system have been determined experimentally at T = (288.15, 293.15, 298.15, 303.15 and 308.15) K. As the temperature decreases, this aqueous two-phase system exhibits a phase inversion. Specifically, the [Bmim]BF4-rich phases are the less dense top phases at high temperatures but become the bottom phase at elevated temperatures. The effect depends on the concentration of both the [Bmim]BF4 and MnSO4. At temperatures of (293.15 and 303.15) K, inversion occurs for the system only at higher concentrations of either phase-forming constituent. In addition, as the temperature increases the inversion-phase region expands. The binodal curves are fitted to an empirical non-linear expression developed by Merchuk, and the salting-out effect at various temperatures was studied quantitatively using the Setschenow equation. (C) 2013 Elsevier Ltd. All rights reserved.