Abstract The phase diagram for the system CaCl 2 KClCaCrO 4 has been determined using differential thermal analysis in conjunction with X-ray diffraction. CaCl 2  KClCaCrO 4 has been shown to be a stable diagonal section of the Ca,K//Cl, CrO 4 reciprocal ternary system. The 3 binary systems are: CaCl 2 KCl which exhibits a congruently melting compound (CaKCl 3 ) melting at 741 °C with eutectics at 24.0 mole % KCl (m.p. 615°C) and 74.3 mole % KCl (m.p. 594°C); CaCl 2 CaCrO 4 which shows a eutectic at 23.4 mole % CaCrO 4 (m.p. 660°C); and KClCaCrO 4 with a eutectic at 24.2 mole % CaCrO 4 (m.p. 651°C). The binary congruently melting compound separates the ternary system into 2 pseudoternary subsystems. A binary eutectic exists in the pseudobinary system CaKCl 3 CaCrO 4 at 12.9 mole % CaCrO 4 (m.p. 672°C). Ternary' eutectics exist at 71.8 mole % CACl 2 -17.3% KCl-10.9% CaCrO 4 (m.p. 575°C) and 23.2 mole % CACl 2 -71.2% KCl-5.6% CaCrO 4 (m.p. 573°C). Isotherms are shown for the liquidus surface (primary crystallization) and for the secondary crystallization surface. Isothermal and vertical sections through the phase diagram are also shown.