A phase diagram of the system A12O3-A14C3 is proposed. Two intermediate oxycarbides, A14O4C and A12OC, were established. Eutectic melting between alumina and A14O4C occurred at 1840° C. No other low melting was observed. The alumina phase was not corundum but was similar to delta-alumina. Because of the high reactivity of aluminum carbide and all the intermediate compounds with moisture and oxygen, use of refractories based on the system A12O3-A14C3 must be limited to applications where these agents are excluded. The behavior of high-alumina refractories in the presence of carbon is explained.