The synergistic effect for a solvent mixture of diisopropyl ether and n-Pentanol to extract hydroquinone from aqueous solution was investigated. Liquid-liquid equilibrium data of the quaternary (n-Pentanol + diisopropyl ether + water + hydroquinone) system were measured at T = 298.15 K and P = 101.3 kPa, using various compositions of solvent mixture. It can be seen from the slope of the tie lines that with the increase of distribution coefficients of hydroquinone, the size of the immiscible solution region decreased slightly. The extraction efficiency was evaluated by calculating the separation factor and distribution coefficient. Using the universal quasichemical (UNIQUAC) and nonrandom two-liquid (NRTL) models to correlate with experimental data, the corresponding binary interaction parameters were obtained. The RMSD values of UNIQUAC and NRTL models showed that the calculated results were in good agreement with the liquid-liquid equilibrium data.