Abstract: The study of rare earth compounds as lubricant additives has become one of the mostinterested research topics for tribochemists,To give full play to the superiority of China'S rich rareearth resources,extensive studies of tribological application of rare metallic compounds have beenconducted.In this paper,the tribOlogical performance of oil soluble europium dialkyldithiophosphate(EuDDP)was evaluated and compared with commercial zinc dialkyldithiophosphate(ZDDP). Thereafter,the tribochemical features of EuDDP were studied through scanning electron microscopy(SEM),energy dispersion analysis of X-ray(EDX),Auger electron spectroscope(AES)and X-ray photoelectron spectroscopy(XPS).The results indicated that EuDDP possesses better lubricationability than ZDDP,This can minly be attributed to the formation of a boundary film containingEu2O3,FeS,organo-sulfide,sulphate,phosphate, etc,and a europium-rich diffused layer whichchanged the critical stress for surface crack to occur.