In this study, the effect of cellulose nanoparticles (CNs) on the corrosion and mechanical behaviour of the biodegradable polylactic acid (PLA) coating was investigated. For this purpose, 1, 5, and 10 wt-% of CNs were added to the PLA coating. By adding CNs to the coating, the corrosion resistance of the PLA coating increased and the highest improvement in corrosion resistance was obtained at 5 wt-% of CNs. Further increase of CNs from 5 to 10 wt-% reduces the corrosion resistance of the PLA coating due to a decrease in the adhesion of the coating to the substrate from 2.4 to 1.6 MNm −2 . Also, the presence of CNs gives higher hardness and better mechanical properties.