Abstract: Organic fluid containing Ag nanoparticles was prepared using extraction-reduction method. Thus Ag~+ was extracted with an extractant Cyanex302 in liquid paraffin and reduced directly therein, to get the liquid paraffin containing the extractant-modified Ag nanoparticles. The tribological behavior of the resulting liquid paraffin fluid containing modified Ag nanoparticles was evaluated on a four-ball machine, using liquid paraffin, liquid paraffin containing the extractant, and liquid paraffin containing Cyanex302-Ag complex as the references. The worn steel surface morphologies were observed on a scanning electron microscope. It was found that the liquid paraffin containing the modified Ag nanoparticles showed much better friction-reducing and antiwear abilities than the base stock and the base stock containing the extractant, which was largely attributed to the load-carrying and antiwear action of the Ag nanoparticles. The steel was characterized by severe adhesion and scuffing under the lubrication of liquid paraffin alone, while the adhesion and scuffing were effectively abated under the lubrication of liquid paraffin containing the modified Ag nanoparticles. The present method to prepare the organic liquid containing metal nanoparticles could be applied to the mass production of organic liquids and lubricating oils doped with metallic nano-particulates.