The liquidus, solidus, and subsolidus in the system MgO‐MgCrz04 were redetermined. Petro‐graphic studies indicated that 47 wt% Cr203 could enter into the periclase lattice at about 235OO C. X‐ray and optical data showed that the solid solution decreased to 32 wt% Cr202 at 2165OC, 11 wt% at 1600°C, 5 wt% at 1400°C, 2.5 wt% at 1200°C, and 0 wt% at 1000°C. Petro‐graphic studies also suggested that picrochromite could contain about 5 wt% MgO in solid solution. The liquidus was much higher than has been indicated on previously published phase equilibri