Absract. In this study, the effect of annealing temperature on physical properties of CdS thin films was studied.  CdS in the form of thin film was prepared by a simple and inexpensive spray pyrolysis technique for various annealing temperatures.  After deposition, films were annealed at 400-450-500 °C for 2 hours at air atmosphere.  The effects of the annealing temperature on the physical properties of the films were investigated by studying the transmittance measurements, spectroscopic ellipsometry technique, atomic force microscope (AFM) observations and the four probe technique.  The transmittance measurements were used to estimate the band gap energy by the linear fit of (ahn)2 curve.  The band gap energy was found to be slightly decreasing with the annealing process.  From the four probe measurement the resistivity was determined and found to be strongly decreasing with increasing the annealing temperature.  Finally, annealing process and annealing temperature confirmed significant effects on the optical, electrical and surface properties CdS thin films.