The sesquicarbide of uranium, , has been found to exist as a stable compound below about 1800°C. At higher temperatures, it decomposes into UC and . It has not been produced directly from the melt but only by heating a mixture of UC and between 1250° and 1800°C. A slight amount of stressing, even as little as that incidental to handling a specimen, is necessary to initiate the reaction. An experimentally determined density of 12.7 g/cm3 agrees very well with a density of 12.88 g/cm3, calculated from x‐ray data. The crystal structure of the compound had been found to be body‐centered cubic, having a space group symmetry I43d and a unit‐cell dimension of .