Solvent-free covalent MXene nanofluids (MXene NFs) were prepared as eco-friendly additives to improve the dispersibility of MXene and the tribological performance of lubricants. Here, the tribological properties and tribo-mechanisms of MXene NFs additives in glycerin and polyethylene glycol (PEG 400) were evaluated, and pronounced differences were observed. In glycerin, the excellent anti-friction (28.9%) and anti-wear (98.0%) properties were realized after 0.5   wt% MXene NFs addition, for MXene NFs preferentially adsorbing onto the surface of friction pair and participating in the formation of tribofilm. However, in PEG 400, the poor friction-reducing and negative anti-wear performance were related to PEG 400 exhibiting high affinity towards steel substrate. This work provides a new approach for fabricating eco-friendly additives with excellent dispersion and lubricity.