Titanium oxynitride thin films were deposited by d.c. reactive magnetron sputtering from titanium metallic target and from oxygen and nitrogen as reactive gases. The nitrogen mass flow rate was maintained constant whereas that of the oxygen was pulsed during the deposition. A constant pulsing period was used and the introduction time of the oxygen was systematically changed from 0 to 100% of the period time. The reactive gas pulsing technique allowed to prepare TiOxNy films with various metalloid concentrations (0 less than or equal to x less than or equal to 2.0 and 0 less than or equal to y less than or equal to 1.0) and led to changes of the crystallographic structure from f.c.c. TiN to tetragonal TiO2. The variations of the metalloid content in the films result in changes in the electrical and optical properties and the reverse evolution of the oxygen and nitrogen content correlates with the transition from metallic to semiconducting behavior. The sputtering conditions were investigated taking into account the poisoning phenomena of the surface of the target from real time measurements of the target potential and from the reactive atmosphere, followed by mass spectrometry. Such diagnostics allowed to understand and to control better the advantageous role of the reactive gas pulsing technique and conducted to close relationships between the process parameters and the film properties.