The purpose of this reaserch is to measure the phase equilibrium data of the ternary system (water + phosphoric acid + 1-nonanol) at different temperatures. Experimental solubility curves and tie-line points for the system were obtained at T = 298.2, 308.2 and 318.2 K and ambient pressure. The binodal curve data were detected by the cloud point method. The mass fractions of each layer were achieved by acid-base and the Karl-Fisher titration, accompanied by refractive index calibration curves. A type-1 LLE phase diagram was observed for this ternary system. The equilibrium tie-line data were correlated via the UNIQUAC and NRTL thermodynamic models. The experimental tie-lines of the studied system were satisfactorily regressed to the models. The reliability of the experimental end points was determined using the Othmer-Tobias and Hand plots. Distribution coefficients and separation factors were calculated over the non-miscible parts. For the separation process, separation factor should be greater than one. For the investigated system, the facor was suitable for separation treatment in all concentrations of phosphoric acid and three temperatures.