Substitution of too expensive alloys rich in noble metals by alloys based on nickel or chromium is often considered in prosthetic dentistry. When containing chromium in quantities high enough the corrosion performances of the “predominantly base” alloys very interesting, as well as their mechanical properties. Such alloys are generally rather complex because of the presence of other elements such as molybdenum, tungsten, silicon and other, which may be active during corrosion and mask the importance of the chromium content. In this work it was chosen to look for a critical chromium content over which the corrosion behaviour is acceptable or very good, by working with simple binary Co-xCr alloys (x varying from 0 to 30 wt.% by slices of 5 wt.%) especially prepared by casting, by avoiding any interference of other elements classically present (Mo, W, Si…). Electrochemical investigations were carried out in a neutral 37°C-heated 9 g/L NaCl solution, classically used in such studies. Follow-up of open circuit potential, application of the Stern-Geary and Tafel methods, and cyclic polarizations allowed identifying 25 wt.% as being a threshold to respect for being certain to benefit from the highest corrosion resistance.