Abstract: The tribological properties of T8 steel pin sliding against Al_2O_3 ceramics disc under the lubrication of 500SN base oil containing various lubricant additives were investigated on a Falex test rig in a pin-on-disc configuration. The worn surfaces of the steel pins were observed on a scanning electron microscope, while the chemical compositions of the worn steel surfaces were analyzed by means of Auger electron spectroscopy. Thus sulfurized cottonseed oil (T405), fatty acid amine salt of benzotriazole (T406), phosphate (T451), tricresyl phosphate (T306), benzene thiophosphate (T309), and sulfurized isobutylene (T321) were tested as the additives in the 500SN oil at a fixed mass fraction of 2% or 0.5% (T406). It was found that all the tested additives functioned to improve the friction-reducing and antiwear abilities of the base stock to varied degrees. T405, T406, and T309 functioned to greatly improve the antiwear ability of the base stock. T306 and T321 had marginal effect on the antiwear ability of the base stock, which could be related to their stronger corrosiveness to the T8 steel. The worn surfaces of the T8 steel pins lubricated with different lubricant systems were characterized by adhesion and scuffing.