In this paper, the water + 1-(2-hydroxyethyl)-3-methylimidazolium chloride ([HOEtMIM]Cl) binary system was studied as a novel alternative working pair of the absorption heat pump cycle. Thermodynamic properties of the system including vapor pressure, density, and heat capacity were measured in the mole fraction range from 0.0122 to 0.3071 of [HOEtMIM]Cl. The vapor pressures of the binary system were determined by the boiling-point method in the pressure from (2.82 to 102.29) kPa and correlated by the nonrandom two-liquid (NRTL) model. The densities and heat capacities were measured in the temperature range from (298.15 to 323.15) K and (298.15 to 358.15) K, respectively, and correlated by the polynomial equations on temperature and concentration. The average relative deviations (ARDs) between the experimental and the calculated values of vapor pressure, density, and heat capacity are 1.42 %, 0.09 %, and 0.38 %, respectively.