Liquid liquid miscibility temperatures as a function of composition have been determined experimentally for the binary systems formed by trihexyl(tetradecyl)phosphonium chloride with hexane, octane, decane, undecane, and dodecane. All the measured systems present solubility curves characterized by asymmetry with respect to equimolar composition and represent the phase diagrams with the upper critical solution temperatures (UCST). For a given set of binary mixtures with trihexyl(tetradecyl)phosphonium chloride, the solubility decreases with increasing alkane chain length. The experimental liquid liquid equilibrium data were satisfactorily correlated by the NRTL equation.