A new technique was proposed in order to improve poor corrosion resistance in magnesium. That is, magnesium hydroxide film was formed on the surface of 3N-Mg by artificial corrosion in 1 % MgCl2 solution for 3.6 ks, which followed by oxidation at 673 K for 3.6 ks in air. Corrosion resistance was evaluated by salt immersion tests in 1 % NaCl solution under in situ laser microscopic observations. Bubble evolution, which occurred immediately at the beginning of the immersion test Q in the case of non-treated specimen, was suppressed by the process. And also, formation of filiform. corrosion was suppressed for about,3.6 ks, which occurred at 180 s in the non-treated specimen.