Abstract Optical constants in the visible region of the spectrum were measured by ellipsometry for polished bulk titanium and for thermally grown oxide layers on the bulk substrates. Experimentally determined values of the instrument angles ψ and Δ are compared with computer-generated values using assumed values of optical constants for the oxide layers and measured values of the optical constants for the film-free titanium substrate. The optical constants obtained for the TiO 2 show only a small variation in n from 2.45 to 2.38 over the wavelength range 576.6–397.1 nm. The oxide films show slight absorption (as reported by Menard) with k varying from 0.23 to 0.25. Reflectance curves for the TiO 2-Ti system are also given.