In this paper, nanocrystalline SnO 2 films are coated on ultrafine Al 2 O 3 particles by hydrolyzing SnCl 4 vapor using fluidization chemical vapor deposition (FCVD) technology. The morphology and distribution of SnO 2 films in Al 2 O 3 agglomerates as well as on ultrafine Al 2 O 3 particles are determined by means of X-ray diffraction (XRD), EPMA, high resolution electron microscopy (HREM) etc. The results show that nanocrystalline SnO 2 films are deposited uniformly throughout the whole agglomerate if Al 2 O 3 agglomerates are fluidized and the films are made up of both amorphous SnO 2 and 6-10nm crystallites on the surfaces of ultrafine Al 2 O 3 particles under different coating conditions. FCVD can be developed into a competitive method for surface modification of ultrafine particles.