The synergistic extraction of phenol from aqueous solution with diisopropyl ether (DIPE) and n-pentanol was studied at 298.15 K under 101.3 kPa. The liquid-liquid equilibrium (LLE) data of the quaternary system (DIPE + n-pentanol + phenol + water) were studied using several proportions of mixed solvents, and the data of the ternary system (DIPE + phenol + water) were supplemented. Compared with single-solvent DIPE or n-pentanol, the extraction effect of the mixture (DIPE + n-pentanol) on phenol was significantly improved. The extraction efficiency was evaluated by calculating the distribution (D) and separation coefficient (S). Furthermore, the experimental LLE data were regressed with NRTL and UNIQUAC thermodynamic models to obtain the corresponding binary interaction parameters. The difference between the calculated value and the experimental value is less than 2%, calculated by relative root mean square deviation, indicating that the calculated and experimental results are in good agreement.