The surface morphology of RF magnetron sputtering Ta2O5 films on Si substrates was studied by X-ray reflectivity measurement and atomic force microscopy. The growth exponent beta was found to be 0.49 +/-0.05 for the polycrystalline films with thickness over 10 nm. During the early stage of polycrystalline Ta2O5 growth, the surface roughness change indicates the development of in island nucleation process and an island coalescence morphology. For the amorphous thin films, the surface roughness was 0.32+/-0.03nm with beta<0.05, which is much smoother than that of the polycrystalline films. It might indicate that Mounds or facet grow on the surfaces of polycrystalline thin films. (C) 2002 Elsevier Science B.V. All rights reserved.