The corrosion properties of STS316L steels and Al coated STS316L steels are studied in aluminum chloride–1-ethyl-3-methylimidazolium chloride ionic liquid, Al sputtering condition. The coated layer condition of each test sample after the RTIL and sputtering process was measured using a SEM. Sputtering is the most widely used high-rate vacuum coating technique to modify surfaces or surface features. So sputtering was successfully formed a good stability and high adhesion coated layer on STS316L. Sputtered STS316L steels were studied at 300-700 oC in (N2/H2O/H2S)-mixed gas condition up to 100 hours. Sputtered STS316L steels corroded slower than un-coated STS316L steels, because of the sputtered STS316L steels consisted primarily of Al coated layer on surface. Its corrosion resulted in the formation of α-Al2O3 and FeAl2S4, Al2S3. However, STS316L steels formed scales were FeS, indicating that sulfidation dominated during corrosion and These sulfides grew via the outward diffusion of Cr, Fe, and Ni, forming voids behind.