The phase relationships in the system //2-CaO were with those in the system HfO//2-CaO. Two ordered phases, CaZr//4O//9 and Ca//6Zr//1//9O //4//4, were found in the system ZrO//2-CaO. CaZr//4O//9 seems to be metastable, and the Ca//6Zr//1//9O//4//4 phase, which is an equilibrium phase, disorders at 1355 degree plus or minus 15 degree C. In the system HfO//2-CaO, three ordered phases were found. The CaHf//4O//9 phase is metastable and decomposes into Ca//2Hf//7O//1//6 and a hafnia solid solution. Ca//2Hf//7O//1//6 and Ca//6Hf//1//9O//4//4 are equilibrium phases in the system HfO//2-CaO. It was confirmed that Zr//3Y//4O//1//2, which appears in the system ZrO//2-Y//2O//3, disorders at 1382 degree plus or minus 5 degree C into a fluorite-type solid solution. This result was used to refine the existing ZrO//2-Y//2O//3 phase diagram. 14 refs.