We prepared several photochromic composite films based on a hybrid organic-inorganic matrix in which metal heteropolyoxometallates are entrapped. Infrared Fourier transform and W-Visible spectroscopic ellipsometry methods have been used for the first time to study the coloring/bleaching process of the: composite films. Data on all samples were acquired using a J.A. Woollam Co. VASE instrument and WVASE software. The optical absorption of these spin-coated films changed markedly by a reversible process, in the presence or absence of UV irradiation. The VIS-NIR transmission data showed that the films containing tungsten heteropolyoxometallate (HPOM) had strong absorptions at about 720 nm, 1108 nm and the films containing molybdenum HPOM had a strong absorption at 720 nm. We have also extracted for the first time the visible and infrared optical functions of the films. For the colored films, the Lorentz and Gaussian oscillators were used to describe the optical behavior in the 400-1700 nm wavelength range and 700-4000 cm(-1) wavenumber range, respectively. The composite films containing tungsten heteropolyoxometallate (HPOM) showed faster coloration and bleaching than pure tungsten oxide films. The composite films with molybdenum HPOM showed faster coloration and much slower bleaching than tungsten HPOM.