The lithium bromide + lithium iodide + lithium nitrate + lithium chloride (mole ratio 5:1:1:2) aqueous solution is a potential working fluid for air-cooled absorption chillers. Three important thermophysical properties were measured: solubility, heat capacity, and density. The solubilities were measured, in the temperature range (276.04 to 353.21) K, using visual polythermal and calorimetric methods. Heat capacities were measured in the range of temperatures from (312.63 to 372.08) K and a range of total salt mass fraction of (0.4953 to 0.6394). Liquid densities were measured at 1.0 MPa from (303.15 to 423.15) K and total salt mass fraction from (0.5150 to 0.6594). In addition, the Young's rule was checked for density predictions in the reported system at (305.15 and 323.15) K and 0.1 MPa. For this purpose, densities of the quaternary salt and lithium iodide aqueous solutions were measured at 0.1 MPa and several temperatures and concentrations. All the experimental data were correlated using empirical polynomial equations.