The chloride-rich part of the ternary system CaCl2-NaCl-CaO has been investigated. Ten vertical cross-sections below 20 mol% CaO were studied by differential scanning calorimetry. A liquidus surface corresponding to primary crystallisation of CaCl2 and three secondary crystallisation lines were determined. The constructed ternary phase diagram was found to be of a simple ternary eutectic type, E=500 degrees C (48 mol% CaCl2, 47 mol% NaCl, 5 mol% CaO)