Zr-B-O coatings were deposited on both construction steel and stainless steel substrates by magnetron sputtering of ZrB2 targets in reactive Ar-O-2 gaseous mixtures. In this paper, the deposition rate and the structural and mechanical properties of Zr-B-O films will be investigated as a function of the inlet oxygen flow rate. We will show that two domains are available owing to the sputtering phenomena. In the former, the coating enrichment is quite proportional to the oxygen how rate. Even for a weak oxygen enrichment, amorphization of the Zr-B-O films is observed which also decreases both their intrinsic internal stress and microhardness, thus improving the physical quality of the coatings. As the oxygen flow rate increases, the amorphous coatings, initially composed of a single-phase ZrB2-xOx solid solution, present an increasing fraction of amorphous ZrO2, and then, of amorphous B2O3 simultaneously with the disappearance of the metallic solid solution. Higher oxygen flow rates allow the synthesis of optically transparent amorphous oxide mixture films, the composition and mechanical properties of which become independent of the inlet oxygen flow rate.