Abstract: A ball on disk friction and wear test rig was used to examine the friction and wear behavior of SUJ2/S45C rubbing pair under oil lubricated condition. The effect of externally applied voltage on the friction and wear behavior was investigated as well. As the results, externally applied voltage shows a significant effect on the friction and wear behavior under the lubrication of nonpolar base stock H60 mineral oil. The effect of the externally applied voltage on the friction and wear behavior is dependent on the additive as well. Namely, externally applied voltage has little effect on the friction and wear behavior under the lubrication of stearic acid/H60, while the effect is considerable under the lubrication of stearic alcohol/H60. The latter is especially so when a positive externally applied voltage was applied. It has been supposed that the minimized effect of the externally applied voltage on the friction and wear behavior under the lubrication of polar additive containing base stock is attributed to the relatively strong adsorption of the polar additive on the lubricated steel surface. This in turn abates the effect of the externally applied voltage on passive state oxide film on the anode metal surface during rubbing.