The aim of this work is to obtain further evidence about the salting-out effect produced by the addition of Na3PO4 to aqueous solutions of water miscible ionic liquid [C4mim][I] by evaluating the effect of Na3PO4 on the thermodynamic properties of aqueous solutions of this ionic liquid. Experimental measurements of density and sound velocity at different temperatures ranging from 288.15 to 308.15 K and the liquid-liquid phase diagram at different temperatures ranging from 288.15 to 338.15 K for aqueous solutions containing [C4mim][I] and Na3PO4 are taken.