Abstract: FeCoCrMnNiN_x high entropy nitride ceramics thin films were prepared using the magnetron sputtering method, and the effects of nitrogen content on the thin films’ properties were later examined. The addition of N₂ affected the microstructures of the thin films and their mechanical and corrosion properties. Compared with the FeCoCrMnNi thin films with 1-sccm N₂, the addition of 2 and 3 sccm of N₂ by as much as 5.45at% and 6.34at% changed the solid solution’s crystalline structure into an amorphous structure. The addition of nitrogen caused drastic changes to the surface morphology, creating a smoother and more uniform surface without cauliflower units. The atomic force microscopy image analysis indicated that the addition of nitrogen reduced the surface roughness from 5.58 to 1.82 nm. Adding N₂ to the CoCrFeMnNi thin film helped increase its mechanical properties, such as hardness and strength, while the Young’s modulus decreased. The hardness of (8.75 ± 0.5) GPa and the reduced Young’s modulus of (257.37 ± 11.4) GPa of the FeCoCrMnNi thin film reached (12.67 ± 1.2) and (194.39 ± 12.4) GPa, respectively, with 1 sccm N₂. The applied coating of the CoCrFeMnNi thin film on 304SUS increased the corrosion resistance, whereas the addition of nitrogen to the CoCrFeMnNi thin film also improved its corrosion resistance compared with that of the CoCrFeMnNi thin film without nitrogen.