Abstract: Carbon nanotubes(CNTs), synthesized by catalytic decomposition of hydrocarbon gases method, can be well dispersed in lubricating oil when they were treated by ball milling. Effects of CNTs as an additive of commercial lubricating oil Great Wall SE 15W/30 on the friction and wear properties have been studied. Worn surface morphology was examined with scanning electron microscopy(SEM), and wear volume was measured with a Talysurf 5P-120 topographer. Results show that CNTs, in mass concentration of 0.01%~0.1%, can greatly improve the antiwear ability of lubricating oil. With addition of CNTs, the maximum reduction of wear rate is about 57%, and scratches on the worn surfaces become slighter and more uniform. The maximum decrease of friction coefficient is about 15% with 0.025% CNTs additive at the load of 300 N. The antiwear mechanism has been discussed.