The dielectric properties of metallic Ti and thin films of TiO2 and TiN in the energy range from 1.5 to 60 eV have been determined by quantitative analysis of the respective electron energy loss spectra in the reflection mode (REELS). The energy loss function (ELF) of every material, that is proportional to Im {1/ε}, is obtained by trial and error until a good quantitative agreement between the simulated and experimental inelastic electron scattering cross‐sections at three different primary electron energies (i.e. 0.5, 1 and 1.5 keV) is achieved. Kramers‐Kronig transformation is then used to obtain real and imaginary parts of the dielectric function ε(ω). In addition, spectroscopic ellipsometry was used to improve the ELF in the 1.5 to 4.5 eV energy range where it is strongly affected by the experimental energy resolution and the presence of the elastic peak. The characteristic differences among the spectra of the particular compounds are discussed in terms of different electronic properties.