This work presents vapor pressure data for water, 1-propanol, and 2-propanol as well as their binary mixtures in the presence of ionic liquid (IL) 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) at different temperatures and IL content ranging from mass fraction 0.10 to 0.70 using a quasi-static ebulliometer method. Activity coefficients of these solvents in the IL have been determined from the vapor pressure data of binary systems and correlated by the nonrandom two-liquid (NRTL) equation with an average relative deviation (ARD) within 0.013. The resulting binary NRTL parameters were used for the prediction of vapor pressure of ternary systems with fair accuracy. Furthermore, the isobaric vapor-liquid equilibrium data for ternary systems water + 1-propanol + [MMIM][DMP] and water + 2-propanol + [MMIM][DMP] at different IL mass fractions were predicted. It is shown that the relative volatility of 1-propanol and 2-propanol is enhanced and that the azeotrope of water + 1-propanol and water + 2-propanol mixtures is eliminated completely.