MEK(methyl ethyl ketone) can be separated from MEK-Water-Toluene azeotropic mixture by azeotropic distillation using the selectivity of entrainer. Acetone was selected as the best entrainer by comparing the ratio between infinite dilute activity-coefficients. Depending on the added amount of acetone and the concentration of MEK-Wa-ter-Toluene mixture, the presence of two phase was identified by UNIFAC model. When acetone was added more than 3.14 times the amount of MEK-Water-Toluene mixture, the mixture formed a single phase and the azeotropic point was eliminated. The optimum amount of entrainer to minimize the plate number was calculated through the simulation of distillation process by UNIQUAC equilibrium model. The number of ideal plates increased with MEK composition and was independent of water and toluene composition. Also, the optimum feed-plate location was calcula-ted at each reflux ratio for various amounts of entrainer, and the minimum reflux ratio was identified as 0.6. For the case that brought Acetone-Water as bottom product and MEK-Toluene as distillate from MEK-Toluene as distillate from MEK-Water-Toluene mixture where the composition of MEK, water and toluene compositions was 40, 30, 30mole%, respectively, 14 ideal plates were required for the best results when the reflux ratio was 0.9% and the ratio of entrainer to feed was 5. The bottom product was composed of 56 mole% of MEK and 44 mole% of toluene and the optimum feed-plate was located between the sixth and the eleventh in this case.