Abstract: Water-soluble nano-silica particles were prepared and characterized by TEM and XRD. Their tribological properties were evaluated using an Optimol SRV IV oscillating friction and wear tester in ambient condition. The frictional mechanisms were also discussed based on the analysis of SEM and XPS results. The results indicated that water-soluble nano-silica particles possessed good anti-wear and friction-reducing properties. It can be concluded that the deposited films formed during friction played an important role.