The antimony nanoparticles with different particle sizes were prepared by mechanical ball milling method while the particles surface was modified by silane coupling agent KH-570. The tribological properties of experimental lubricating oil, which are 900SN and others lubricating oils containing antimony nanoparticles with various particle size，were studied by reciprocating friction experiment in CFT-1 material performance tester. The worn surface morphology and chemical composition of 45 steel were analyzed by SEM and EDS. The results show that antimony nanoparticles play a role in repairing effect for worn surface basing on micro-filling and adhesion mechanism. With decreasing of particle size of antimony nanoparticles and increasing of frication load, the antifriction and antiwear properties of experimental lubricating oils increase. The experimental lubricating oil containing antimony nanoparticles with 40 nm of particle size has good antifriction and antiwear properties under higher friction load.