Electron beam gun technique was used to prepare Ta2O5 thin. films onto infrasil substrates of thicknesses 333 and 666 nm. The structure characterization was investigated using X-ray diffraction patterns. Transmittance measurements in the wavelength range (240-2000 nm) were used to calculate the refractive index n and the absorption index k depending on Swanepole's method. The dispersion curve of the refractive index shows an anomalous dispersion in the absorption region and a normal one in the transparent region. The analysis of the optical absorption data revealed that the optical band gap E-g was indirect transition. It was found that the refractive index dispersion data obeyed the single oscillator of the Wemple-DiDomenico model, from which the dispersion parameters (E-o and E-d) and the high frequency dielectric constant were determined. The electric free carrier susceptibility and the carrier concentration to the effective mass ratio were estimated according to the model of Spitzer and Fan. Graphical representation of the relaxation time as a function of photon energy was also presented. (C) 2008 Elsevier B. V. All rights reserved.