Abstract: Rare earth elements and their compounds have been found increasing applications in improving the structure and texture of metals and increasing the wear resistance and load bearing capacity by chemical heat treatment to metals or other physical techniques.In recent years,some inorganic rare earth salts were shown to be good solid lubricants.In order to overcome the difficulty of dissolving inorganic rare earths into lubricating oils,an oil soluble cerium dioctyl dithiocarbamate was prepared as an antiwear and extreme pressure additive,its chemical structure was characterized by infrared spectroscopy and inductively coupled argon plasma spectroscopy,and its tribological performances were evaluated with a ring on block test rig and a four ball machine.In addition,tribochemical characteristics of the additive under boundary lubrication conditions was studied by means of AES and XPS.The results showed that the additive can obviously increase antiwear and EP performances,and decrease the friction coefficient of the basestock over 30%.While the surface layer formed by the additive was actually composed of organic film,oxidation film,chemical reaction film and permeating film.The friction induced permeation of cerium played an important role in modifing the surface structures of rubbing pairs and increasing the wear resistance.