Abstract: The wear mechanisms of metal by nitrile rubber under boundary lubrication condition were investigated.The morphology of wear track and chemical state of elements in worn metal and rubber surfaces were examined by SEM and XPS.The function groups in rubber were analyzed with FT IR.It was found that the rubber molecular chain was broken at the site of stress concentrations.The broken molecular chain generated active macromolecular free radicals that reacted with the activated iron atoms and generated metal polymer film on the metal surface.Meanwhile,the mineral oil formed physical and chemical absorption film.The boundary lubricating films on metal surface were destroyed by repeating shear stress and the debris on the sliding surface.The removal of the boundary lubricating film contributed to the wear of metal by rubber.