Abstract: The wear mechanisms of AISI1020 steel by natural rubber under dry sliding were investigated. Thus the original and worn surface morphologies of and the elemental compositions and chemical states of the steel and rubber were observed and analyzed by means of scanning electron microscopy equipped with energy dispersive X ray analysis attachment and X ray photoelectron spectroscopy. The functional groups on the original and worn surfaces of the natural rubber were analyzed by means of Fourier transform infrared spectroscopy. It has been found that the wear of AISI1020 steel by natural rubber is mainly characterized physically by interfacial adhesion, while chemically by mechanochemical reactions between the surfaces of the steel and natural rubber, accompanied by the surface oxidation of the steel. The iron atoms and oxides on the steel surface react with the macroradicals of the natural rubber, therefore the products such as Fe polymer compound and ferrous oxide polymer complex are generated. Moreover, at the subsurface of the steel, the activated iron atoms react with the macroradicals and produces Fe polymer complex. The main oxides on the steel surface are Fe 2O 3, FeO and Fe 3O 4, while that at the steel subsurface is FeO. This is because the transfer film on the steel surface helps to restrain the oxidation of the steel. Moreover, the transfer film of different characteristics as compared with the steel substrate is also effective to reduce the friction and wear of the steel, by keeping off the direct contact between the rubbing surface of the steel and the natural rubber and restraining the abrasive action of the wear debris.