In this work, glycolic acid was separated from glycolonitrile hydrolysate by an extractant consisting of tri-n-octylamnie, tri-n-butyl phosphate, n-octanol, and sulfonated kerosene. In a single equilibrated apparatus, the synergistic effect of the extractant, the influence of diluents composition, the temperature, and the concentration of ammonium sulfate in the hydrolysate on the distribution coefficient of glycolic acid were studied. The extractant loading of glycolic acid was back-extracted by pure water at high temperature. The results show that synergistic effects appear below 1.56 mol . L-1 of glycolic acid. When the concentration of glycolic acid is higher than 3.42 mol . L-1, there is either little or no synergism effect. The quantity of ammonium sulfate in the hydrolysate has little effect on the extraction efficiency. Based on material balance, a mathematical model for the synergistic extraction was established. In a Phi 50 mm Kuhni extraction column, glycolic acid was separated continuously from the hydrolysate.