In absorption cycles, ionic liquid (IL) 1,3-dimethylimidazolium tetrafluoroborate ([Dmim]BF4) may be a promising absorbent of working pair using water as refrigerant. The vapor pressures of [Dmim]BF4 aqueous solution were measured with the boiling-point method in the temperature range from 312.25 to 403.60 K and in the mass concentration range of 65% to 90% of [Dmim]BF4. The experimental data were correlated with an Antoine-type equation and the Non-Random Two-Liquid (NRTL) model, and the average absolute deviations between the experimental and calculated values were 1.06% and 1.15%, respectively. For the [Dmim]BF4 aqueous solution, the experimental vapor pressures show negative deviations from the calculated data with Raoult's law. For higher mass concentration of the IL, the deviation is more negative. In addition, the vapor pressures, the hydrophilicity and the solubility of [Dmim]BF4 aqueous solutions were compared with those of [Dmim]Cl aqueous solutions and [Bmim]BF4 aqueous solutions at IL-mole fraction of 0.20.