The present study analyzes the use of TiO₂ layer as antireflection coating. TiO₂ thin films were prepared on silicon substrate by electrochemical anodization process with thicknesses of 130 and 170 nm. The films exhibit a uniform nanotubular structure. The ellipsometry measurement data were analyzed using a multi-layer model, the bottom layer is a dense layer of TiO₂ and the top layers are porous; they are formed by a mixture of TiO₂ and void. The values of refractive index are obtained by the Bruggeman effective medium approximation. The refractive indexes of the bottom and top TiO₂ sublayers were about 2.3 and 1.6, respectively. The lower values of reflectance are obtained with the thinnest film. For these samples the reflectance decreases about 90% compared to silicon and in some cases the reflectivity is less than 5%. The thickness influences of TiO₂ thin films and their synthesis parameters on the optical constants are discussed.