Recently, ionic liquids (ILs) have received an increasing attention as lubricants owing to their intriguing properties such as tunable viscosity, high thermal stability, low emissions, non-flammability, and corrosion resistance. In this work, we investigate how the incorporation of octadecyltrichlorosilane (OTS) functionalized silica nanoparticles (NPs) in 1-butyl-3-methylimidazolium (trifluoromethysulfony)imide, influences the tribological properties and rheological properties of IL under boundary lubrication and elastohydrodynamic conditions, respectively. It was found that the coefficient of friction depended on the concentration of NPs in IL with a concave upward functional trend with a minimum at 0.05 wt.% for bare silica NPs and at 0.10 wt.% for OTS-silica NPs. For steel-steel sliding contact, the presence of functionalized nanoparticles in IL at the optimum concentration decreased the coefficient of friction by 37% compared to IL and 17% compared to IL with bare silica NPs. While IL with bare NPs demonstrated a shear thinning behavior for all concentrations, IL with functionalized NPs showed a Newtonian behavior at low concentrations and shear thinning behavior at high concentrations. Overall, this study provides new insights into the anti-friction and anti-wear additives for lubrication systems involving ionic liquids.