Abstract: Water soluble Cu nanoparticles are synthesized by in situ surface modification with NH₂-functionalized magnesium silicate hydroxide and characterized. The morphology of as-prepared Cu nanoparticles is observed on a transmission electron microscope. The conductivity coefficient of the aqueous solution of Cu nanoparticles is measured with a thermal conductivity coefficient surveying instrument. An Optimol SRV Ⅳ (ball-on-block) oscillating friction and wear tester and is performed to evaluate the tribological properties of Cu nanoparticles in water. Results indicate that as-prepared Cu nanoparticles have good friction-reducing and anti-wear properties for steel-steel frictional pair. In the meantime, as-prepared Cu nanoparticles can reduce the conductivity coefficient of pure water by nearly 10%, which is beneficial for as-prepared Cu nanoparticles to function as a kind of water-based lubricating additives.