Ti-B-N nanocomposite coatings were deposited on silicon, glass and steel substrates by DC magnetron sputtering of a TiB2 target in various Ar-N-2 reactive mixtures. In this report, some optical properties of the films were investigated in connection with their structure. At low nitrogen flow rate, coatings contain nanocrystals of titanium diboride. On the other hand, at high nitrogen flow rate, only titanium nitride nanocrystals are detected by grazing angle X-ray diffraction. Whatever the nitrogen flow rate, Fourier-transform infrared spectroscopy shows the occurrence of an amorphous boron nitride phase. Moreover, the number of B-N bonds continuously increases with the nitrogen flow rate, even if the boron and nitrogen concentrations in the film become nearly constant. Colour measurements show a progressive decrease of the coating brilliance vs. the nitrogen flow rate. Thus, Ti-B-N nanocomposite coatings are suitable for decorative applications. The UV-visible transmittance of Ti-B-N coatings increases with the nitrogen flow rate due to an increase in the number of B-N bonds. Finally, the shape of the transmittance curve for a Ti-B-N coating is similar to that of a TiN coating, as soon as TiN nanocrystals are detected in Ti-B-N coatings.