Effect of di-tert-dodecyl disulfide as an additive on decomposition of MAC oil on the nascent surface of bearing steel 52100 was investigated. After the removal of surface contamination layer, active sites were generated, on which tribochemical decomposition of MAC oil occurred. The additive prolonged the induction period of the decomposition. Hydrogen and gaseous hydrocarbons desorbed as tribochemical reaction products. Desorption rate of hydrogen and gaseous hydrocarbons increased proportionally with sliding velocity and linearly with the cube root of load. XPS analysis revealed tribochemical reaction between additive and nascent surface occurred, which induced formation of iron sulfide and decrease of activity of nascent surface. As a result, decomposition of MAC oil decreased correspondingly.