Two types of functionalized polyaniline (PAN) were synthesized based on the interfacial polymerization. PAN was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy and Fourier transform infrared spectrometer. The results showed that synthesized PAN had different structures and was effectively modified by ionic liquids. The tribological properties of PAN as additives in polyethylene glycol (PEG) for steel/steel pairs were investigated in detail. The maximum reduction in friction and wear was achieved by PEG with addition of 0.2 wt% PAN. In particular, the wear volume was reduced by 3.8 times under 200 N. Moreover, the lubrication mechanisms were proposed by SEM and X-ray photoelectron spectroscopy (XPS) analysis of the worn surfaces.