Zinc-coating and tin-coating have been used for improvement of the corrosion resistance of steels. Magnesium alloys of less noble metal could be also used as the sacrificial anodes. In this study, the extruded compacts composed of magnesium and Sm₂Co₇ of magnetic alloy were brought into contact with SS400 steel through the magnetic force of Sm₂Co₇, and the effect of their sacrificial anode was investigated by using the potentiodynamic polarization test, the corrosion test under constant quantity of electricity, the ICP measurement for the dissolved elements and the surface analysis on the specimens by XPS. The sacrificial anodic effect of the magnesium alloy with Sm₂Co₇ could not be recognized. However, the suppression of corrosion rate by magnesium alloy with Sm₂Co₇ brought into contact with steels was observed. This result suggests that the magnesium alloy is effective for the improvement of the corrosion resistance of steels.