To improve the performance of an absorption system, ionic liquids (ILs) have been chosen as additives to conventional working fluid (lithium bromide aqueous solution) in recent years. In this paper, 1-ethyl-3-methylimidazolium acetate ([Emim]Ac) was added to lithium bromide aqueous solution (mass ratio LiBr/[Emim]Ac = 3) to measure the vapor-liquid equilibrium (VLE) data of the ternary system. The experiment was conducted by means of boiling point method, at temperatures between 303.94 K and 405.41 K and mass fractions of absorbent between 0.20 and 0.60. The experimental data were regressed using an Antoine-type equation, and the average absolute relative deviation (AARD%) between the experimental and calculated values was 0.34%, which showed excellent accuracy and consistency. The experimental ternary system was compared with the conventional LiBr + H2O system and two other ternary systems from the literature; the result revealed that the experimental ternary system had lower vapor pressures, which will benefit the process of releasing latent heat in absorption cycles.