Tantalum ethoxide [Ta(OC2H5)5] and water vapor (H2O) are used as chemical precursors to deposit Ta2O5 thin films on K9 and JGS1 substrates by atomic layer deposition (ALD) at the temperature of 250 ℃ and 300 ℃ respectively. Characteristics of the films such as optical properties, microstructure and surface morphological image are investigated by spectrophotometer, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and atomic force microscopy (AFM). The results show that both the as-deposited and annealed Ta2O5 films are amorphous. The film deposited at the temperature of 250 ℃ possesses excellent microstructure with good optical properties in the spectral region from mid-ultraviolet to near-infrared, and it can be well used for optical coatings as a kind of high-refractive-index materials.