Abstract: Environmental friendly and biodegradable lubricant has been a significant research focus for the purpose of reducing environmental pollution, and some plant constituents have been utilized as lubrication additives.Plant leaves are known to be covered by thin wax layer, which was called plant leaf-surface wax or plant epicuticular wax.Plant leafsurface wax is a mixture of organic material including alkanes, alcohols, esters, and acids, which have proved to be good lubrication additives.Based on this, wheat leaves were selected as research object.The tribological properties of wheat leaf- surface wax as additives were evaluated on MFT- R4000 reciprocating friction and wear tester.The tests were conducted on steel-copper friction pair, and the friction coefficient was recorded automatically by a computer connected to the MFT-R4000 tester, the wear volume of worn surfaces was measured by a surface profilometer.The morphologies and element constitution of worn surfaces were observed and examined using scanning electron microscope (SEM) and energy- dispersive X- ray spectroscopy (EDX), respectively.The results showed that poly- α- olefin (PAO) containing wheat leaf- surface wax had excellent tribological properties.In the case of friction coefficient, PAO containing wheat leaf-surface wax as additives showed lower and more stable friction coefficient on steel-copper friction pair than other additives.Its average friction coefficient was reduced by 25% compared with the pure PAO, and its friction reduction property was close to MoDTC.Compared with PAO or PAO containing MoDTC, glycerin, and stearic acid, the wear volume of wheat leaf-surface wax was almost reduced by 70%.Obviously, wheat leaf-surface wax possessed superior anti-wear performance compared with MoDTC and stearic acid, and was similar to glycerol.The SEM results showed that PAO with wheat leaf- surface wax had fewer scratches, shallower grinding crack, and smaller edge roughness compared with pure PAO.The worn surface of PAO mixed with stearic acid and glycerol was similar to that of PAO with wheat leaf- surface wax, but deeper and clearer.Gas chromatography- mass spectrometry (GC-MS) method was used to analyze wheat leaf- surface wax constitution, and the results showed that wheat leaf- surface wax was mainly composed by fatty alcohol and fatty acid.As such, fatty alcohol content in wheat leaf-surface wax was about 54.3%, the carbon chain length mainly ranged between C20-C30 and concentrated on C26 and C27.The majority of alcohols were straight chain fatty alcohol, and some had annular structure.Meanwhile, wheat leaf- surface wax also included alkane and the corresponding content was about 19%, and the carbon chain length ranged between C21-C30.Fatty acid of the wheat leaf-surface wax was about 2.6% in content.The test results also showed most carbon chains owned odd number of carbon atoms.The alcohols, acids and other natural ingredients mixture in wheat leaf- surface wax can form a protective adsorption film on the worn surface.The esterification reaction also performed on the worn surface.The protective adsorption film was the reason for the improved friction reduction and anti-wear properties of lubricant on steel- copper friction pair.This research provides a reference to the study of extracting excellent green biodegradable additive from plants, and also has a great significance for economically utilization of plant leaves.