Structure and optical characteristics of nickel ( Ni ) single crystal (100) surface and thin films have been evaluated by the combined use of reflection high-energy electron diffraction (RHEED) and spectroscopic ellipsometry (SE). Nickel films were fabricated by thermal evaporation at 100°C while Ni single crystal was grown by vertical Bridgman method. RHEED analysis indicates that the grown Ni films were polycrystalline. Spectral dependencies of refractive index n(λ) and extinction coefficient k(λ) determined in the spectral range λ ~ 250–1030 nm indicate the typical behavior of metals. The refractive index of Ni films is found to be slightly higher compared to that of Ni (100) crystal.