Potentiodynamic polarization and E (corr) versus t curves were obtained, together with electrochemical impedance spectroscopy (EIS) measurements, in order to understand the effects of alternating voltage (AV) passivation on the corrosion resistance of duplex stainless steel (DSS). SEM, EDS and XPS were employed to further investigate the influence of AV passivation on the properties of the passive film. The results of the electrochemical measurements showed that AV passivation significantly improved the corrosion resistance of DSS. SEM images indicated that the surface exhibited a unique morphology after AV passivation treatment, and XPS results suggested that AV passivation greatly increased the thickness of the passive film. Furthermore, significant chromium enrichment and a higher ratio of Fe3+/Fe2+ were observed in the passive film after AV passivation. Mott-Schottky results confirmed that AV passivation had a strong influence on the semiconducting properties of the passive film.