Dimethyl sulfoxide (DMSO) solvent is widely researched in Li-O₂ battery due to its stable cycling performance compared to other solvents. However the instability of a Li metal in contact with DMSO is still concerned. Therefore, the effect of the solid electrolyte interphase (SEI) on a Li anode on the charge-discharge cycling performance in 1 M LiTFSI in DMSO is examined using charge-discharge cycling. The chemical structure on the surface of the SEI is revealed to strongly affect the cycling performance of a lithium metal anode. A low coulombic efficiency, which is less than 75 %, is observed when the organic compounds such as lithium alkyl carbonates (ROCO₂Li) and polycarbonate are mainly formed on the surface. However, when the inorganic compounds such as Li₂CO₃ and Li₂O are formed in place of the organic compounds, the enhanced coulombic efficiency, which is over 85%, is obtained. In order to prevent side reactions with the electrolyte during cycling in 1 M LiTFSI/DMSO, the lithium surface should be protected by inorganic compounds prior to the cycling.