Liquid-liquid phase equilibria (LLE) for the system of water/tert-butyl alcohol (TBA)/2-ethyl-1-hexanol were investigated experimentally at different temperatures of 298.15. 303.15, 308.15, and 313.15 K. A type I liquid-liquid phase diagram was obtained for this ternary system. These results were correlated simultaneously by the UNIQUAC model. The values of the interaction parameters between each pair of components in the system were obtained for the UNIQUAC model using the experimental results. The root mean square deviation (RMSD) between the observed and calculated mole percents was 2.58%. The mutual solubility of 2-ethyl-2-hexanol and water was also investigated by the addition of TBA at different temperatures.