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This study investigated the effects of the electric potential of a surface on the lubricating capabilities of ionic liquids. The friction coefficient of 1-butyl-3-methylimidazolium iodide was unchanged by the electric potential of the surface because this ionic liquid has difficulty moving in a solution owing to its low conductivity. However, the friction coefficient, when lubricated with 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate and 1-butyl-3-methylimidazolium hexafluorophosphate, changed when the electric potential of the surface was varied. At -2.0 V, cations were adsorbed on the sliding surface. The alkyl chain of cations supported the load and achieved a low friction coefficient. However, at 2.0 V, anions were adsorbed on the sliding surface. Such ions cannot support the load, and thus reach a high friction coefficient.