Phase equilibria in the CeO2-CoO system at temperatures above 1500degreesC were investigated. The microstructures and the phase compositions of the DTA (differential thermal analysis) samples and the quenched solid pellets were analyzed using SEM (scanning electron microscope), EDX (energy dispersive X-ray), and WDX (wavelength dispersive X-ray). A eutectic reaction was found at 1645 +/- 5degreesC. The eutectic point was calculated to be at 82 +/- 1.5 mol% CoO. The eutectic phases were the CeO2-rich phase (containing <5 mol% CoO) and the CoO-rich phase (containing similar to0.5 mol% CeO2). At 1580degreesC, the solubility of CoO in CeO2 was similar to3 mol%.