In this study, corrosion phenomena of PEO-treated films formed in solution containing Mn, Mg, and Si ions were researched using various experimental instruments. Ti-6Al-4V ELI disk (grade 5, Timet Co. Ltd, Japan Diameter; 10 mm) was used as a specimen for plasma electrolytic oxidation (PEO) treatment. The specimen was cleaned and used as an anode, and a platinum rod was used as a cathode in the electrolyte containing Mn, Mg, and Si ions for PEO process. The potentiodynamic polarization and AC impedance tests for corrosion behaviors were carried out in 0.9% NaCl solution. The surfaces of the PEO-treated Ti-6Al-4V specimens were observed by a field emission scanning electron microscopy (FE-SEM, S-4800 Hitachi, Japan) and energy dispersive X-ray spectroscopy (EDS). In the case of PEO-treated surface in electrolyte containing Mn ions, precipitates of Mn were mainly formed on around the pore, and the number of pores decreased, as Mn contents increased. From the result of potentiodynamic test, the corrosion potential of PEO-treated surface in solution containing Mn ion was higher than that of in solution containing Mg ion. In the case of PEO-treated surface in electrolyte containing Mn ions, second anodic peaks showed in the passive region. From the AC impedance test, in the case of 5Mg5Mn/5Si specimen, polarization resistance is higher than those of other specimens. (C) 2018 Elsevier B.V. All rights reserved