The inclusion complex of βcyclodextrin(βCD)and dibutyl phosphite(T304)was prepared by trituration.The tribological properties of the complex with different concentrations were investigated by a fourball tester in the solution of polyethylene glycol600(PEG600).The tribological test results show that the complex exhibits better friction reducing and antiwear properties than βCD under different loads,that is because that the complex is decomposed into various molecular fragments and the T304 molecules are released under the friction condition.The tribosystem shows the least friction coefficient when the concentration of the complex is 09%.The XPS analytical results on the worn surfaces reveal that phosphide films formed by the released T304 play a major role and the iron alkoxide and carbon deposition films formed by the βCD fragments have better friction reducing effect on the phosphide film surface.The interactions of different films result in the formation of a mixed boundary lubrication film.