Solubilities of halite in the ternary system NaCl-CsCl-H2O have been determined by the visual polythermal method at 1 atm from 20 to 100 °C along five constant CsCl/(CsCl + H2O) weight ratio lines. These five constant weight ratios are 0.1, 0.2, 0.3, 0.4, and 0.5. The maximum uncertainties in these measurements are ±0.02 wt % NaCl and ±0.15 °C. The data along each constant CsCl/(CsCl + H2O) weight ratio line were regressed to a smooth curve. The maximum deviation of the measured solubilities from the smooth curves is 0.06 wt % NaCl. Isothermal solubilities of halite were calculated from smoothed curves at 25, 50, and 75 °C.