Needle coke wastewater is rich in phenol and poses a great challenge to industrial implementation of phenol extraction because of the low extraction capacity of current industrial extractants. In this paper, the synergistic extraction of phenol from aqueous solution with a mixture of methyl isobutyl ketone (MIBK) and n-pentanol (n-PTL) was investigated. Liquidliquid equilibrium data of the quaternary system (MIBK + n-PTL + phenol + water) was measured at 298.2 K and 101 kPa by varying the compositions of synergistic solvents. The results show that it performs the highest distribution coefficient, as the ratio of MIBK and n-PTL reaches 8:2 by the low mass fraction of phenol in the aqueous phase. The tie-line lengths are calculated to estimate the size of the immiscibility zone. The root-mean-square deviations (RMSDs) show that the regressed results are well consistent with the experimental data when correlating with nonrandom two-liquid (NRTL) and universal quasichemical (UNIQUAC) models, and the corresponding binary interaction parameters are obtained.