A single wavelength ellipsometry and cyclic voltammetry measurements were simultaneously used for the investigation of oxide growth on copper in 0.1 M NaOH solution. These investigations were part of joint research of electric and physical properties of cuprous and cupric oxide during layer formation and growth. This type of joint impedance and ellipsometric study has not been performed before. In this paper, authors discuss composition of multilayer film structure using various models and fitting methods enabling interpretation of multilayer oxides structure formation during passivation process. It is shown that implementation of effective medium approximation allows to obtain an accurate model fitting, using Levenberg–Marquardt optimization algorithm and mean square error.