The behavior of a Pt electrode/solution of lithium perchlorate and lithium hexafluorophosphate in a γ-butyrolactone (GBL) interface has been investigated by using in situ FTIR spectroscopy and single reflection ATR-FTIR spectroscopy. The bands due to free GBL and GBL solvated to lithium ions in the solution were confirmed by the single reflection ATR-FTIR spectra. The dependence of potential on the concentration of GBL and solvated GBL in the vicinity of a Pt electrode was investigated. In the FTIR spectra, the reversible changes in the concentration of free GBL and solvated GBL in the diffuse double layer were observed with change in potentials. As the potential decreased, the free GBL concentration increased, while the concentration of the GBL solvated to lithium ions decreased. The reverse phenomenon was observed as the potential increased. Thus, it can be concluded that the equilibrium shifts from Li+(GBL)4 to Li+(GBL)3 and GBL as the potential decreases. It became clear for low potentials that the product material contained lithium ions in irreversible reactions.