Abstract: Oil soluble Bi nanoparticles with an average diameter of 60 nm were successfully prepared from bulk bismuth by solution dispersion. The morphology of the resulting nanoparticles was observed on a transmittance electron microscope, and the effect of the synthetic nanoparticles as an additive on the friction-reducing and antiwear behavior of liquid paraffin was investigated on a four-ball tester. The worn steel surface was observed on a scanning electron microscope and the elemental composition thereon determined on an energy dispersive spectrometer. It was found that Bi nanoparticles as the additive contributed to greatly improving the friction-reducing, antiwear,and load-carrying capacity of the base stock, and to effectively abating the scuffing of the frictional pair as well. However, no Bi was detected on the worn steel surface by EDS analysis. Therefore it was suggested to carry out further work so as to reveal the action mechanisms of the Bi nanoparticles as the additive.