We studied on the phase equilibria of quaternary liquid-liquid extraction system containing 1-propanol-water-binary solvent at 25 ℃, 1atm, butyl acetate-o-xylene was used as binary solvents. Binodal curve, tie-line, distribution and selectivity for each quaternary system have been determined in order to investigate the effect of using binary solvent in extracting 1-propanol from aqueous solution. And these experimental tie-line data were also compared with the values predicted by UNIFAC model. It was shown that UNIFAC model is capable of predicting the tie-line in these quaternary systems whithin an average RSDM of 1.45 mole%.