Ionic liquids (ILs) are increasingly expected to be used as lubricants or additives in industry as they feature many attractive properties. The interaction effects between ILs and traditional additives become significant for future application. This paper investigates the synergistic effects of 2-Mercaptobenzothiazolate based ILs and Mo nanoparticles in polyethylene glycol (PEG) base oil. The hybrid additives outperform neat PEG oil and PEG with single additives. Surface analyses (SEM-EDS, Raman, XPS, cross-sectional TEM-EDS) demonstrate that MoS2 formed in the tribofilm, which is a critical factor to the observed excellent tribological properties. The outcomes of this work can not only provide fundamental insights into the formation of the tribofilm, but also promote the industrial application of ILs as lubricating additives.