The pseudodielectric-function spectra, epsilon(E)=epsilon(1)(E)+iepsilon(2)(E), of polycrystalline Cd0.96Zn0.04Te thin films in the 1.3-5.5eV photon energy range at room temperature were obtained using spectroscopic ellipsometry. The measured dielectric-function spectra reveal that distinct structures at energies of the E-1, E (1)+Delta(1), and E-2 critical points are due to interband transitions. The Cd0.96Zn0.04Te thin films investigated were deposited by vacuum evaporation under a pressure better than 1.3 x 10(-3) Pa onto well-cleaned glass substrates kept at 300 K. The films exhibited zinc blende structure with predominant (111) orientation. The root mean square (r.m.s.) roughness of the vacuum-evaporated Cd0.96Zn0.04Te thin films evaluated by ex situ atomic force microscopy is 3.7 nm. Dielectric-related optical constants, such as the refractive index (n), extinction coefficient (k), absorption coefficient (alpha) and normal incidence of reflectivity (R) determined from the spectroscopic ellipsometry data are presented and analyzed. The optical constants of the films were also determined using optical transmittance measurements and the results are discussed. (C) 2002 Kluwer Academic Publishers.