The complex dielectric function of CdTeO(x) and CuCdTeO thin films was determined by spectroscopic ellipsometry in the photon energy range of 1.5 to 5 eV. The films were grown onto glass slides substrates by reactive rf co-sputtering using CdTe and Cu targets in an Ar + O(2) atmosphere. Films with different Cu concentrations were obtained by varying the power on the Cu target. The dielectric function of the films is represented by a generalized Lorentz harmonic oscillator expression. Three-dimensional type line-shapes for the critical points E(1) and E(1) + Delta(1) of CdTe were identified in CdTeO(x) and CuCdTeO films even for Cu and O concentrations above 20 at.%. This latter result can be indicative of CdTe alloying with those elements widening the possibilities for new photovoltaic materials. (C) 2010 Elsevier B.V. All rights reserved.