The work aims to study structure-function relationship between molecular structure and tribological/physico chemical properties of aryl-substituted aromatic acid ionic liquids (ILs). With 4-methylphenylacetic acid (4-Me-PA), 4-tert-butylphenylacetic acid (4-tBu-PA), 4-phenylbutyric acid (PB) and ibuprofen sodium salt (Ibu) as anion sources, and tetrabutylammonium hydroxide (N4444OH), tetrabutylammonium chloride (N4444Cl), 1-butyl-3-methylimidazolium chloride (C4mim), 1-octyl-3-methylimidazolium chloride (C8mim) as cation sources, seven aryl-substituted aromatic acid ILs were synthesized based upon acid-base neutralization and ion exchange reaction. The structure-activity relationship between molecular structure and tribological/physicochemical properties of ILs was systematically investigated with commercially available synthetic poly-alpha-olefin (PAO 10) and 1-butyl-3-methylimidazolium tetrafluoroborate (L-B 104) as control samples. These ILs exhibited good hydrolysis stability, high thermal stability, and no corrosion to metallic substrates. Thermal decomposition temperature of the ILs ranged from 161 to 217 ℃, and pH value of hydrolysis reaction remained unchanged. Average friction coefficient f and average wear volume V of the three pairs was fsteel/steel=0.081, fsteel/copper=0.067, fsteel/aluminum=0.080, Vsteel/steel=3.24×10?3 mm3, Vsteel/copper=22.04×10?3 mm3, Vsteel/aluminum=22.35×10?3 mm3, respectively, when being applied to steel/steel, steel/copper and steel/aluminum friction pairs. These ILs had good anti-friction and anti-wear properties, and their molecular structure had significant effects on tribological/physicochemical properties. In the aryl-substituted aromatic acid ionic liquids, the longer the substituted alkyl chain is, the higher the thermal decomposition temperature is, the higher the kinematic viscosity and viscosity index are. The larger the space volume of anions is, the higher the viscosity index of corresponding ion liquids is. These ILs exhibited good lubrication on steel/steel, steel/copper, and steel/aluminum friction pairs, mainly owing to the formation of a stable adsorption film on the friction pairs. The anions and cations in the film have different effects, cations play a major role in reducing friction, while anions play a major role in resisting wear. The lubricating property is also affected by viscosity, the ILs with appropriate kinematic viscosity and high viscosity index exhibit more excellent tribological properties.