1. Metallographic analysis showed that new phases are formed in high-cerium cast irons (cerium concentration above the optimal). 2. X-ray analysis indicates the presence of cerium compounds with iron in hypoeutectic cerium cast irons-CeFe2 and CeFe5-and also CeC2. The quantity of these phases increases with the cerium concentration of the alloy. 3. In high-cerium cast irons the cerium actively interacts with the components of the cast iron in the early stages of solidification, forming Ce2C3. 4. The variation of the ferrite lattice constant with the cerium concentration of cast iron as-cast and after annealing points to the solution of cerium in α iron.