► Comparison between Ce(III) and Ce(IV) salts as inhibitors of AA2024 corrosion. ► Both of cerium salts could react as corrosion activators or inhibitors as well. ► Oxides/hydroxides formed during inhibition by Ce(III) cover all cathodic sites. ► Ce(III) deposits contain Ce3+ and Ce4+ species but these of Ce(IV) have only Ce3+. ► The inhibition efficiencies of Ce(III) solutions are higher than those of Ce(IV). The corrosion protection of the AA2024 aluminum alloy in 0.01M NaCl solutions of Ce(III) and Ce(IV) ammonium nitrates was studied. The inhibition efficiency was evaluated applying linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Superficial analytical techniques (optical microscopy, SEM, EDS and XPS) were applied for elucidation of the inhibition mechanism. The results showed that both cerium salts could behave either as inhibitors or activators of the corrosion process depending on the experimental conditions. The solutions of Ce(III) salt revealed better inhibitive ability than those of Ce(IV) in a relatively large range of conditions.