Se90Te10 Ag-x(x)(0 <= x <= 6) compositions were prepared by quenching technique. Thin films with different thicknesses of the obtained compositions were deposited on dry clean glass substrates by thermal evaporation technique. Energy dispersive X-ray spectroscopy (EDX) indicates that samples are nearly stoichiometric. X-ray diffraction patterns indicate that they are in the amorphous state. The optical constants, the refractive index n and the absorption index k, have been calculated from transmittance T and reflectance R through the spectral range of 400-2500 nm for the studied films with different thicknesses (165-711 nm). From the analysis of refractive index n data, high frequency dielectric constant epsilon(infinity) was determined. Both epsilon(infinity) and n are found to decrease with the increase of Ag content. The optical band gap E opt g is calculated for all compositions from the absorption coefficient analysis. The effect of the Ag addition on the obtained optical parameters has been discussed. The analysis of absorption index k data, revealed the existence of allowed indirect transitions for all compositions. It is indicated also that E opt g increase with increasing Ag content. (C) 2008 Elsevier B. V. All rights reserved.