In this study, cerium was investigated as an inhibitor to improve the corrosion resistance of ASTM A915 mild steel in 0.1 M NaCl solution. Increasing the Ce3+ concentration up to an optimum level of 600 mg.L-1 (or 1.4.10(-3) M) sharply decreased the corrosion rate (I-corr). However, the beneficial effect of cerium was lost after short immersion times at room temperature. In contrast, the addition of polyethylene glycol (PEG) to the cerium nitrate containing NaCl solutions enhanced protection through the formation of stable corrosion products and the decrease of cracks in the film formed on the surface of mild steel.