Three mixed lithium greases with different mass percent of graphene oxide(GO) additive were prepared by using the basic oil of castor oil and the thickening agent including lithium hydroxide monohydrate,12-hydroxystearic acid and sebacic acid.The physicalchemical properties and lubricating performance of mixed lithium greases were investigated by means of the penetration tester,the steel mesh oil separator tester,the dropping point tester,the rheometer,the thermogravimetric analyzer,the frictional tester and the threedimensional surface profilemeter.The mechanism between castor oilbased grease and GO was also discussed.The results show that with the increase of shear rate and temperature,the viscosity of mixed lithium greases containing GO shows a trend of nonlinear reduction,but the GO plays a smaller and smaller role on the relation between the viscosity and shear rate of castor oilbased greases and the viscositytemperature characteristics.The moderate amount of GO can improve the thermal stability of mixed lithium greases.With the increase of the GO mass percent,the average coefficient of friction of the mixed lithium base grease is decreased first and then increased.The moderate amount of GO is helpful to improve the friction reducing and antiwear ability of castor oilbased grease,this is because GO enters the contact area of the friction pair in the form of sheet layer,which can effectively reduce the direct contact probability of the friction pair surface,and GO has the selflubricating property,which plays a more effective lubrication role on the interface of the friction pair.