The ultrafine powder of lanthanum oxide with D₅₀<10 μm was prepared by using the lanthanum chloride solution as raw materials which was under industrial production of extraction,separation and purification.The effects of calcination temperature,dispersant type,pH of the solution on the particle size of lanthanum oxide powder during the preparation process were investigated.The size distribution of samples were measured with laser granularity instrument,the samples were charac-terized by X-ray diffraction and scanning electron microscopy.The results showed that the ultrafine lanthanum oxide powder with uniform particle size and good dispersibility could be prepared under acidic reaction conditions with calcination tempera-ture of 750 ℃,calcination time of 2 h and adding dispersant PEG2000 with mass fraction of 1%.