Lead selenide thin films of thicknesses between 80 to 250 nm, are prepared by thermal evaporation under vacuum of -1.3 x Pa. X-ray diffraction studies reveal the formation of polycrystalline films. The optical gap is determined as a function of film thickness. It is observed that the width of the optical gap lies between 0.3 to 0.4 eV, additionally it shows the tendency t o decrease with increasing film thickness. Ellipsometry is used to estimate the optical constants and the absorption coefficient. Two well defined peaks are observed at energies of about 1.8 and 2.9 eV. The data are analysed in the frame of the band structure of PbSe,.