Optical constants of cadmium sulfide (CdS) thin films for different bath temperature were determined in the spectral range, 400 to 1200 nm from the optical absorption and transmittance measurements. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), techniques was used to determine the crystallite structure and morphology of the films. EDX images showed that a sample with 70 degrees C bath temperature had a stoichiometric composition. The crystallite size and microstrain were calculated using Williamson-Hall method. Optical study is performed to calculate the refractive index (n), extinction coefficient (k), optical conductivity (sigma), dielectric constant (real and imaginary), and optical band gap using transmission spectra. (C) 2010 Elsevier B. V. All rights reserved.