Abstract: To study the influence of different precursors on rare earth oxide, corresponding precursors were prepared, and lanthanum oxide was obtained through calcination, with sodium bicarbonate, ammonium bicarbonate and oxalic acid as precipitants and lanthanum chloride as lanthanum source. The effect of precursor on the morphological structure of lanthanum oxide was then explored with TG, XRD, FT-IR, granularity analysis, SEM and ICP as analytical characterization means. The results showed that during the precursor roasting there were three weightless stages, respectively corresponding to the separation of water (crystalline water and adsorption water), the detaching of some CO₂ and further separation of CO₂ until the quality remained the same to form a stable final product, which was lanthanum oxide after being detected by XRD. The median diameter D₅₀ of the precursor after precipitant reaction was respectively 43, 113 and 200 μm. Lanthanum oxide with oval shape, flocculent surface and spherical shape could be obtained after the precursor was calcined. The median diameter D₅₀ was respectively 12, 40 and 52 μm and the contents of La₂O₃ were 95.21%, 95.92% and 97.09% therein in turn. The crystallinity and granularity of rare earth carbonate and lanthanum oxide prepared with carbonate as precipitant were smaller than those of precursor and lanthanum oxide prepared with oxalic acid as precipitant, whose reason was that the rare earth carbonate k_sp was smaller than that of oxalate, resulting in the faster reaction speed of rare earth carbonate. So the aggregation rate of Yin and Yang ions nucleated and then deposited into precipitated particles was faster than the directional arrangement of structural crystal ones, thus forming amorphous fluffy flocs with small particles. The crystallinity, granularity and morphology of the final product are all related to its precursor. The superiority of the precursor in crystallization and granularity would be reflected in the final product, indicating that the precursor has a certain heredity in crystallinity and granularity for the final product.