Amorphous thin films of TbFe, sputter-deposited on quartz substrates with compositions supporting polar Kerr magneto-optical behavior and overcoated with a transparent protective layer, are studied to determine their dielectric tensor elements. Reflectivity measurements over a range of angles of incidence are made in an apparatus that corrects for the overcoat layer and exploits magnetization reversal to enhance the measurement of r// PERPEND , the complex reflectivity associated with the magneto-optical signal. Conventional Fresnel reflectivities are also found. The theoretical model for reflectivities from a thick film magneto-optical medium at oblique incidence is developed and used within a Lavenberg-Marquardt nonlinear estimation algorithm to estimate sequentially the dielectric tensor elements, considering their widely varying magnitudes and sensitivities to errors in reflectivity data. The interpretation of the dielectric elements in terms of magneto-optical performance and structural perpendicular anisotropy is discussed.