Normal incidence ellipsometry has been used to measure the change in the complex anisotropic reflectance ratio ¿ upon oxidation of the clean Si(110)16 × 2 surface. The spectroscopic change in the amplitude of ¿ (tan(¿)) shows a broad maximum of height 1.4 × 10¿3 in the high energy region above 2.5 eV. No phase shift difference for the reflectance coefficients belonging to the surface principal optical axes has been measured. A Kramers-Kronig transformation of the amplitude ratio showed that a change in the phase is not expected. The change in tan(¿) indicates that the change in reflection upon oxidation in the optical region ismainly in the (10) direction.