This research investigates the effect of cerium ion addition on the efficiency of a 3-mercapto-propyl-trimethoxysilane (PropS-SH) coating formed on AZ31 magnesium alloy. The coating was obtained by dipping AZ31 coupons in a hydroalcoholic 3-mercapto-propyl-trimethoxysilane solution, added with cerium nitrate, in order to obtain a 5 x 10(-3) or 5 x 10(-4) M Ce(+3) ion concentration. The silane baths were regulated at pH 4 and utilized for filming treatment after 48 h following their preparation. The treated specimens were finally cured for 1 h at 100 degrees C. The protective efficiency of cerium modified and unmodified PropS-SH coatings was evaluated by recording potentiodynamic polarization curves and electrochemical impedance spectra in a 0.1 M NaCl environment. In comparison to PropS-SH coating, cerium nitrate modified silane layer exhibited noticeably improved performances, in particular in presence of a 5 x 10(-3) M Ce(3+) concentration. The increased protectiveness and stability of the modified coatings were attributed to a lower porosity and defectiveness and to self-healing ability provided by Ce(3+) ion presence. (C) 2011 Elsevier B.V. All rights reserved.