The effect of hydrogen sulfide ions (HS-) on the passivity of type 316L stainless steel was investigated in pH 8.4 boric acid-borate buffer solution. Galvanostatic polarization of a silver microelectrode covered with Ag2S generated both OH- and HS- above the stainless steel surface. During potentiostatic polarization of the stainless steel, the passivity-maintaining current density increased with increase in the concentration of HS- in the vicinity of the surface. The impedance of the stainless steel at a constant frequency decreased during polarization in the presence of HS-, while it was sustained after dilution of HS-. Electrochemical impedance spectroscopy (EIS), Mott-Schottky (M-S) analysis and scanning electrochemical microscopy (SECM) showed that a defective and n-type semiconductive passive film was formed in the solution containing HS-. Auger electron spectroscopy (AES) revealed that metal cations and oxygen vacancies in the passive film on the stainless steel increased when it was formed in a HS- -conoining solution. The series of changes in passive film properties is thought to be due to adsorption of HS- on the film surface during the polarization. (C) The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licensestby/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.