Abstract: The mechanisms of wear of AISI 1020 steel by natural rubber under boundary lubrication condition were investigated. The morphology of wear track as well as the content and chemical state of elements on the worn surfaces of steel and natural rubber were analyzed by means of scanning electron microscopy and X ray photoelectron spectroscopy. The functional groups on natural rubber surface were analyzed with Fourier transform infrared spectrometry. It has been found that the wear of AISI 1020 steel by natural rubber is dominated by micro cutting in terms of physical effect. It is also characterized by the surface oxidation of the steel and the mechanochemical reactions among the steel, natural rubber and mineral oil, in terms of the chemical effects. The main oxides on the worn surface of the steel include Fe 2O 3, FeO and Fe 3O 4. The iron oxides on the worn steel surface may react with the macromolecular chains of natural rubber containing oxygen group, the oxidized alkane chains, and the active sulfur in the mineral oil molecules. Subsequently the products including iron polymer compound and iron metal oxide polymer complex were generated on the sliding surface.