Abstract: Three kinds of inorganic nanoparticles were selected to prepare polymer/inorganic nanocomposites with different interfacial structure. The antiwear and friction-reducing properties and mechanisms of the nanocomposites as additives in AN 10 oil were investigated. The principle on the tribological functional design of polymer/inorganic nanocomposite additives was explored. Results indicated that the polymer/inorganic nanocomposites consisting of inorganic nanoparticles with good tribological behavior were good lubricating additives for AN 10 oil lubricated steel-steel contact. The polymer/inorganic nanocomposites with optimized interfacial structure possessed considerably improved tribological properties as compared with those without optimized interfacial structure. This is because the polymer/inorganic nanocomposites with optimized interfacial structure had good compatibility between the polymer matrices and inorganic nanoparticles, and the inorganic nanoparticles were more uniformly distributed in the polymeric matrices. During friction process, highly active inorganic nanoparticles exposed onto the sliding surfaces along with the decomposition of polymeric matrices by frictional heat and shearing gave birth to protective layers with excellent tribological properties.