The aim of this paper is to study the synthesis of Sn-benzotriazole (BTA) composite nanoparticles by chemical reduction and the tribological properties of the Sn-BTA composite nanoparticles as lubricant additives. The Sn-BTA composite nanoparticles are produced through the reaction of Stannous, Sodium hydroxide, Boron sodium cyanide and BTA in aqueous ethanol solution. BTA functions as the stabilizer of the Sn nanoparticles and the protector of anti-oxidation of Sn nanoparticles in various concentrations. In this process, we do not need extra inert gases to protect the oxidation of Sn nanoparticles. Compared to paraffinic base oil, epoxidized soybean oil has good lubrication characteristics, high viscosity index, low volatile degrees and high flash points. Due to its biodegradable and renewable, epoxidized soybean oil is considered to be an excellent lubricant .The tribological experiments are conducted by using the pin-on-disk test to observe the wear scar diameter, the friction force, and the morphology of worn surface. To investigate the effects of epoxidized soybean oil and paraffinic base oil for tribological characteristics. Their anti-wear and the performances of their anti-friction are found. Finally, OM, SEM and EDS are used to interpret the possible lubricating mechanisms of the anti- friction and the anti- wear. The possible mechanisms of Sn-BTA composite nanoparticles in process of triobological experiments were generalized. Results show that the mean diameter of synthesized Sn-BTA composite nanoparticles is about 19.86nm spherical shape particle in the best percentage of dosage and synthesis condition. The tribological performance of lubricating oils can be improved significantly by dispersing Sn-BTA composite nanoparticles in liquid paraffin oil and epoxidized soybean oil. The friction force and the wear scar diameter which added Sn-BTA in liquid paraffin oil have been reduced by 17% and 53.9% respectively compared with liquid paraffin oil. The friction force and the wear scar diameter which added Sn-BTA in epoxidized soybean oil have been reduced by 19.2% and 54.3% respectively compared with epoxidized soybean oil.In conclusion, the significant finding show that the tribological mechanism is that a deposit film in the contacting regions was formed, which prevented the direct contact of rubbed surfaces and greatly reduced the friction force between contacting surface. Besides, the spherical shape of Sn-BTA composite nanoparticles functioned as rolling ball between the rubbed surfaces.