Isobaric vapor-liquid equilibrium (VLE) at atmospheric pressure (101.3 kPa) for the binary systems of acetone + methanol, acetone + phosphate ionic liquids (ILs), and methanol + phosphate ILs, and for the ternary system of acetone + methanol + phosphate ILs are measured using a circulation VLE still. The phosphate ILs include 1,3-dimethylimidazolium 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]), 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]), and 1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][DBP]). The addition of these phosphate ILs to the azeotropic acetone + methanol system results in a salting-out effect on acetone and makes the azeotropic point disappear. The relative volatility alpha(12) of acetone over methanol increases with increasing molar fraction of ILs. The equilibrium data were well fitted by the electrolyte nonrandom two-liquid model (epsilon-NRTL). Compared with some reported ILs previously such as pyridinium hexafluorophosphate, imidazolium trifluoromethane sulfonate and imidazolium dicyanamide, such imidazolium phosphate ILs are fluorine-free, are prepared more simply with lower cost, and make the azeotropic point disappear at less added amount of ILs. This work shows that such phosphate ILs are a class of potential solvents to separate azeotropic acetone + methanol system.