Bi2Ti2O7, thin films have been grown directly on n-type GaAs (1 0 0) by the chemical solution decomposition technique. Xray diffraction analysis shows that the Bi2Ti2O7, thin films are polycrystalline. The optical properties of the thin films are investigated using infrared spectroscopic ellipsometry (3.0-12.5 mum). By fitting the measured ellipsometric parameter (Psi and Delta) data with a three-phase model (air/Bi2Ti2O7/GaAs), and Lorentz-Drude dispersion relation, the optical constants and thickness of the thin films have been obtained simultaneously. The refractive index and extinction coefficient increase with increasing wavelength. The fitted plasma frequency omega(p) is 1.64 X 10(14) Hz, and the electron collision frequency gamma is 1.05 X 10(14) Hz, and it states that the electron average scattering time is 0.95 X 10(-14) s. The absorption coefficient variation with respect to increasing wavelength has been obtained. (C) 2003 Elsevier Science B.V. All rights reserved.