pulsed laser deposition; La0.5Sr0.5CoO3 films; spectroscopic ellipsometry; optical constant; (LSCO) conductive metal oxide films were prepared on Si (100) suhstrates under different growth temperatures by using pulsed laser deposition (PLD). X-ray diffraction (XRD) analysis shows that the crystallinity of the LSCO films increases with the increase of substrate temperature, and the films deposited at 650℃ and 700℃ are polycrystalline with a single perovskite phase. The optical properties of the LSCO films were measured by spectroscopic ellipsometry in the wavelength range of 400 - 1100nm. Double Lorentz oscillator dispersion relation and a three layer model (Air/ LSCO/Si) were used to fit the optical constants of the films. The results show that the refractive index of the LSCO films decreases as the substrate temperature increases. Extinction coefficient of the LSCO films increases as the substrate temperature increases in the visible and near-infrared wavelength range. It is found that the crystallinity of the films and conductivity are mainly responsible for these phenomena.