Two lithium-based ionic liquids (ILs, L-C3N3, and L-P3N3) were synthesized and evaluated as novel lubricant additives for multiply alkylated cyclopentanes (MACs). They were found to be approximately 1.0% soluble in MACs at room temperature (RT), whereas traditional ILs, such as 1-ethyl-3-methylimidazolium tetrafluoroborate (L-B102), 1-hexyl-3-methylimidazolium hexafluorophosphate (L-P106), and 1-ethyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide (L-F102), could not be dissolved in this base oil. Friction tests indicated that these ILs exhibit excellent friction-reducing and anti-wear properties both at RT and at 100 ℃. They can improve the tribological properties of MACs at RT to a greater extent than the commonly used lubricant zinc dialkyldithiophosphate (T204), even at a concentration of 0.1%. The load ramp test showed that MACs with L-C3N3 and L-P3N3 also exhibit high load-carrying capabilities. Scanning electron microscope (SEM) and X-ray photoelectron spectrometer (XPS) results indicated that physical adsorption and complex tribochemical reactions occurred between the ILs and metal surfaces during the sliding process, thereby forming a surface protective film that significantly contributed to the excellent tribological properties of the new ILs.