he lithiumbased grease was prepared by using carbon nanotubes as an additive,and the effects of additive content,diameter and length of the tubes on the tribological properties were investigated.The results show that carbon nanotubes can obviously improve the tribological properties of lithiumbased grease.With the increasing of the mass fraction of carbon nanotubes,the tribological properties of grease are first increased and then decreased.When the mass fraction of carbon nanotubes is 0.05%,the grease has the best tribological properties.The grease exhibits better tribological properties when adding the carbon nanotubes with small diameter and large tube length.This is because carbon nanotubes with small diameter and large tube lengths may be more easily filled into the grooves of the surface asperities.XPS analysis results show that there are iron oxide and carbon nanotubes in the lubricating film,and the boundary films such as iron oxide and carbon nanotubes play the role of frictionreducing and antiwear properties.