The lubrication behavior of SUS440C stainless steel and dispersion stability of the wear debris in ethanol solution of oleic acid and in n-undecane solution of oleic acid were investigated. The lubrication behavior of SUS440C stainless steel was examined by using pin-on-disk machine. The addition of oleic acid resulted in decrease in friction of SUS440C stainless steel both in ethanol and in n-undecane. Wear of SUS440C stainless steel in ethanol was increased by the addition of oleic acid, while in n-undecane it was decreased. Compounds derived from oleic acid were detected on the SUS440C stainless steel surface worn in n-undecane solution of oleic acid by scanning electron microscopy observation and X-ray photoelectron spectroscopy measurement, while they were hardly detected on the surface worn in ethanol solution of oleic acid. In ethanol solution of oleic acid, corrosive wear and abrasive wear of SUS440C stainless steel seemed to proceed. In n-undecane solution of oleic acid, friction polymer derived from oleic acid seemed to act as a boundary lubrication film. The dispersion stability of iron particle in ethanol solution of oleic acid was higher than that in n-undecane solution of oleic acid. Therefore, wear debris in n-undecane solution of oleic acid seemed to deposit on the sliding surface more easily than in ethanol solution of oleic acid.