Zr–Si–N films were deposited on silicon and X38CrMoV5 steel substrates by sputtering composite Zr–Si targets in reactive Ar–N2 mixture. The silicon concentration in the deposited films was adjusted by the variation of the number of Si chips located on the target erosion zone. As a function of the silicon content, the films exhibited the following structures: insertion of Si into the ZrN lattice, nanocomposite (nc-ZrN/a-SiNx) and an amorphous-like structure. Addition of silicon into ZrN-based coatings induced a lost of the golden aspect due to the decrease of the metallic behaviour. This result was confirmed by ellipsometric measurements. The films refractive index increased with the silicon concentration. On the other hand, a continuous decrease of the extinction coefficient was noticed. The effect of the silicon content on the optical properties of Zr–Si–N films was discussed as a function of the films structure and the occurrence of new optical absorptions due to the silicon chemical bonds. Finally, the evolution of the films electrical resistivity was discussed in connection to the films structure changes.