We report that by the addition of water vapor into the working gas, crystalline tantalum pentoxide (Ta2O5) thin films can be fabricated at low substrate temperatures. At 500degreesC, by the addition of water vapor, the crystaffinity of the thin films was obviously improved. The grains with tetragonal structure were clearly observed by, AFM. Total transmission greater than 85 % was achieved between wavelengths of 400 and 800 nm and the optical absorption edge of the thin films also shifted to smaller wavelength. Our data suggest that the crystallinity of the thin films can be improved and the crystallized temperature can be decreased with the introduction of water vapor in the fabrication process. The effects of water vapor on the crystallization of Ta2O5 thin films are discussed in details. (C) 2004 Elsevier B.V. All rights reserved.