Abstract: An esterified epoxide lubricating oil additive, "DE film forming agent" was synthesized using oleic acid and epoxy resin in this pa- per. Using liquid paraffin or mineral oil as base oil, the effect of DE film forming agent on the tribological properties of lubricating oil was studied on a pin-on-disk tester and a four ball tester. The results shown that the tribological characteristics of lubricating oil are obviously improved after adding DE film forming agent; as compared with the epoxy resin, fatty acid ester or oleic acid,the DE film forming agent can reduce the friction coefficient, the surface scratching demage and wear as well as increase the load carrying capacity of system. The functional mechanism of friction polymeric film formed on the friction surface was also discussed.