The nanocrystalline thin films of CdSe are prepared by thermal evaporation technique at room temperature. These thin films are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and photoluminescence spectroscopy (PL). The transmission spectra are recorded in the transmission range 400-3300 nm for nc-CdSe thin films. Transmittance measurements are used to calculate the refractive index (n) and absorption coefficient (alpha) using Swanepoel's method. The optical band gap (E-g(opt)) has been determined from the absorption coefficient values using Tauc's procedure. The optical constants such as extinction coefficient (k), real (epsilon(1)) and imaginary (epsilon(2)) dielectric constants, dielectric loss (tan delta), optical conductivity (sigma(opt)), Urbach energy (E-u) and steepness parameter (sigma) are also calculated for nc-CdSe thin films. The normal dispersion of refractive index is described using Wemple-DiDomenico single-oscillator model. Refractive index dispersion is further analysed to calculate lattice dielectric constant (epsilon(L)). (C) 2012 Elsevier Ltd. All rights reserved.