Abstract: The metamict allanite from South China is studied by using microscopy, DTA and X-ray powder analyses. The results show that the annealed sample heated to 800 ——850(3 gives the standard X-ray data of allanite, and the sample heated over 850℃ is decomposed. The annealed sample heated to 970℃ is decomposed into cerianite, hematite, anorthite and small amount of allanite and other minerals. From the X-ray powder data the reaction process may be expressed as: 2(Ca, Ce)(Fe). X-ray powder data of the anneaied allanite heated to 11000(2 show that the allanite was decomposed into dominant cerianite, hematite, and anorthite, but allanite disappeared.