Herein, the corrosion behaviour of coated 304 stainless steel in 3.5 wt-% NaCl solution was investigated. Thin films, composed of NbN and Nb x Al y N with different Al contents, were synthesized by magnetron sputtering. The microstructural investigation involved testing in energy-dispersive X-ray spectroscopy, scanning electron microscopy and grazing incidence X-ray diffraction, revealing films with a thickness of 165-200 nm composed of an NbN-δ cubic phase. Corrosion resistance was assessed by potentiodynamic polarization and electrochemical impedance spectroscopy tests. According to the present results, in the proposed the experimental conditions, the addition of Al to NbN coatings is detrimental to the corrosion resistance of coated 304 stainless steel. The Nb 0.90 Al 0.10 N sample shows the lowest corrosion protection and the highest porosity among the studied samples.