Wear tests of the unimplanted and Mo ion-implanted pure iron specimens were made on an SRV fretting wear machine under lubricating condition. The lubricants were liquid paraffin with or without additives containing one or more of the active elements Cl, S, P and Zn. After wear tests, the worn surfaces of the specimens were analyzed by means of Auger electron spectroscopy and X-ray photoelectron spectroscopy. The results showed that Mo ion implantation had a marked effect on friction, wear and tribochemical behavior of the specimen. When the specimens were lubricated with oil containing different additives, the increase in wear resistance due to ion implantation showed different values. This is because the physical and mechanical strengthening caused by Mo ion implantation only is one factor influencing wear behavior. Another wear-effect factor will be the lubricating film which is composed of adsorbed additive and reacted products when the wear specimen is lubricated with oil containing additive. However, Mo in the specimen decreased the chemical reactivity of the specimen surface and obstructed its formation.