Lu(NH 4 )(C 2 O 4 ) 2 ⋅2H 2 O has been successfully fabricated by the improved oxalate precipitation method. Its thermal stability and decomposition behaviour were investigated by using scanning electron microscopy, thermalgravimetric-differantial scanning calorimetry and in situ high temperature X-ray diffraction measurements. Despite substantial removal of oxide, carbon, nitrogen, and hydrogen elements, the scanning electron microscopy images clearly revealed that the precursor calcined Lu 2 O 3 products maintained well the morphology properties of the precursor. Moreover, TG-DSC analysis demonstrated that the peak temperatures of the precursor to Lu 2 O 2 CO 3 and Lu 2 O 2 CO 3 to Lu 2 O 3 were 400 • C and 630 • C, respectively. Finally, and most importantly, the in situ XRD results exhibited that the 'Lu(NH 4 )(C 2 O 4 ) 2 ', 'Lu 2 O 2 CO 3 ' and 'Lu 2 O 3 ' crystal structures formed by heating the Lu (680∼980• C, respectively. The experimental results provided an interesting fact that Lu(NH 4 )(C 2 O 4 ) 2 ⋅H 2 O has been completely decomposed into cubic phase Lu 2 O 3 crystal at 680 • C, which is nearly 200 • C lower than that of lutetium oxalate tetrahydrate prepared by traditional oxalic acid precipitation process.