The optical properties of amorphous PbZr0.52Ti0.48O3 thin films on vitreous silica and sapphire substrates by the RF magnetron sputtering method have been investigated by transmittance measurements. For a single-layer thin film on the transparent substrate, the inverse synthesis or fitting method with the six fitting parameters was given and used to calculate the optical constants such as the refractive index n, the extinction coefficient k, and the absorption coefficient alpha. The film thickness d, which was one of the fitting parameters, is simultaneously obtained. According to Tauc's law, the optical transition in amorphous PbZr0.52Ti0.48O3 thin films is direct in nature. The direct band gaps of amorphous PbZr0.52Ti0.48O3 thin films on vitreous silica and sapphire substrates were found to be 3.36 and 3.25 eV, respectively. The dispersions of the refractive index in films were studied by considering a single-oscillator model. (C) 2003 Elsevier Science B.V. All rights reserved.