Spectroscopic ellipsometry was used to determine the optical properties of plate-like hydrated tungsten trioxide (3WO(3)center dot H2O) films in the energy range 300-4000 cm(-1). Films with different thicknesses were deposited on glass substrates pre-coated with fluorine-doped tin oxide via an efficient and simple hydrothermal method. Parametric models were used to extract thicknesses and optical constants of the thin films. The WO3 was found to be more hydrated for thicker films. Moreover, the nano-plates are larger in thicker films, which leads to a decrease of the transmission due to an increase of the scattering. Features in the obtained dielectric functions of the 3WO(3)center dot H2O thin films were compared with the earlier published optical spectra of WO3 and its hydrates 1/2WO(3)center dot H2O and WO3 center dot H2O. (C) 2014 Elsevier B.V. All rights reserved.