Fully recrystallized ultra-fine grained 316L steel with different grain sizes were prepared by high-energy ball milling followed by hot isostatic sintering. The relationship between grain sizes and the corrosion behaviors in salt water was studied. The results showed that the re-passive ability was always stronger for finer grained samples by formation of much denser and shallower pits, however, the influence of grain size on the pitting potential was insignificant and the passive film even seemed to become susceptible to cathodic polarization when the grains were refined to sub-micron scale. It was notable that there existed many contradictory conclusions in relevant studies. The ambiguity in the relationship between grain size and corrosion behaviors of stainless steels was discussed in detail.