The corrosion behavior of two Fe-Cr-Ni alloys in eutectic nitrate (NaNO3/KNO3) salt and its vapor were investigated at 565˚C for 28 days. Results show higher corrosion rates in salt vapor than in liquid salt. In addition, the surfaces of samples exposed to vapor were severely corroded with spallation of the outer oxide layer. The oxide layer of the corroded alloys in molten salt exhibited lower Cr depletion in comparison with the surface exposed to the vapor salt. The alloy formed a loose double layer of Cr, Fe and Na oxide in molten salt vapor. The oxidation of material in the molten salt vapor contributed the most to the overall corrosion of the sample, and its Cr-depleted depth was nearly twice that of a sample immersed in molten salt. Alloy (chromium) dissolution from the metal into salt and selective oxidation at the salt/metal interface dominates the corrosion mechanism in liquid and vapor salt. This confirms the need to take into consideration the corrosion of alloy by salt vapor during practical material selection process for such applications.