Fluorescence and phase transitions of a new Mg-Al-Eu ternary layered double hydroxide (LDH) and their dependence on thermal treatment were studied for the first time. Phase transitions occurred as the temperature increased from 400 to 1100°C. The process of phase transition is discussed in detail. The emissions of Eu3+ ions described by the 5D0–7FJ transition (J = 1,2,3,4), and especially for the 5D0–7FJ transition (J = 1,2) varied markedly with phase transformations from LDH, MgO, to mixtures of MgO and MgAl2O4. Moreover,strong emissions of Eu3+ ions are present in these new host materials. These results indicate that Mg-Al-Eu ternary LDH may be a potential candidate for materials applied in fluorescent devices.