The corrosion behaviors and mechanisms of 310S and AL-6XN stainless steels in MgCl2 molten salts were investigated at 800°C for 8-72h. The weight change kinetics, surface and cross-sectional morphologies as well as corrosion products and compositions were analyzed. The results showed that corrosion velocities of both steels were very high in the preliminary period, then diminished quickly and trended to zero afterward. The AL-6XN steels exhibited better corrosion resistance in MgCl2 molten salts than 310S. The predominant peaks of MgO were detected from both steels after corrosion in molten MgCl2 at 800°C, which could serve as the protective barriers between the alloy and the MgCl2 molten salts. The depletion of Cr was very serious throughout the corrosion layer for both steels due to their preferential oxidation for the formation of an outer corrosion layer. The other elements in alloy were corroded in succession through the outward diffusion with the progress of the corrosion. The outward migrations of the metal ions led to the coalescence of vacancies to form the voids. The two steels possessed the uniform corrosion behavior.