Most of lubricant additives used as friction modifier and anti-wear agents are mainly organic compounds containing sulfur and phosphorus. Their lubrication mechanism is based on a tribochemical reaction leading to tribofilm formation but also the formation of some harmful by-products. Inorganic nanoparticles could be envisaged for the replacement of such organic additives. A study on the tribological properties of different kinds of nanoparticles added and dispersed as additives to a lubricating base oil was carried out. Added to a poly-alpha-olefin base oil, all nanoparticles showed a reduction of both friction and wear of steel counterfaces. One percent of nanotubes was sufficient to obtain good tribological properties. A structural modification of nanoparticles during friction was observed. In the case of nanotubes, flake-like wear debris made of amorphous carbon were observed. This is an abstract presented at the World Tribology Congress III (Washington, DC 9/12-16/2005).