Abstract: Grain size could significantly affect the mechanical properties, corrosion resistance and failure mode of metals. The changes of corrosion resistance and failure mode were usually attributed to passive films formed on metal surface. In this paper, the effects of grain size on chemical characters, structure, and semiconducting properties of passive films, as well as on films growth/repair and broken were reviewed. In passive environment, the decreasing of grain size increased the concentration of grain boundary, and accelerated the growth and repair of passive films. The defect concentration in passive films also decreased with grains size decreasing. Grain refinement could promote the stability of passive films and therefore improved corrosion resistance of metals.