A new series of tricresyl phosphate (TCP)-based ionic liquids (ILs) were synthesized by mixing TCP with lithium bis(trifuoromethylsulfonyl) imide (LiTFSI). Their tribological properties in pentaerythritol ester were nvestigated using an Optimol SRV oscillating friction and wear tester. LiTFSI/TCP (0.75/1 molar ratio, TCPL3) exhibits the best friction-reducing and antiwear properties under given experimental conditions. Compared with conventional lubricant additive TCP, TCPL3 could signifcantly improve the tribological properties of polyol ester, especially under high-temperature condition. Worn surfaces were analyzed using scanning electron microscope (SEM) and X-ray photoelectron spectrometer (XPS). Surface analysis demonstrates that the outstanding lubricating properties are attributed to the formation of boundary flm which is composed of iron fuoride, lithium phosphate, and lithium polyphosphates.  nexpectedly, a remarkable synergistic efect between TCPL3 and typical high-temperature antioxidant N-phenyl-α-naphthylamine in terms of antioxidation property was also observed.