Abstract: In this study, five kinds of ionic liquids were synthesized with quaternary ammonium, quaternary phosphonium or alkyl imidazolium as cations and dioctyl sulfosuccinate as anions. The physicochemical properties of these ionic liquids were investigated. The tribological performances of these ionic liquids as lubricants for steel/magnesium alloy friction pairs were evaluated by SRV-V oscillating friction and wear tester, where the conventional ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (L-F104) was used as a reference sample. And the lubrication mechanisms of these ionic liquids were also investigated by the characterization of the contact resistance during friction tests, surface morphologies and element state on the worn surfaces. 　The results show that the viscosities of the five dioctyl sulfosuccinate ionic liquids at 40 ℃ and 100 ℃ are higher than that of the reference sample L-F104, especially at 40 ℃. With the increase of cationic alkyl chain length, the viscosity of dioctyl sulfosuccinate ionic liquids basically decrease, which may be due to the large volume of cations, weakening the interaction between the anions and cations in the ionic liquids. The viscosity indexes of the synthesized ionic liquids are higher than that of the LF104. The viscosity index increased with the increasing of the alkyl chain in cation. It can be concluded that the synthesized dioctyl sulfosuccinate ionic liquids have better film formation properties and viscosity-temperature performance than the reference sample L-F104. From the thermogravimetric results, both the synthesized ionic liquids and the L-F104 exhibit well thermal stability, which start to decompose above 200 ℃. However, the thermal stability of the dioctyl sulfosuccinate ionic liquids is lower than that of the L-F104. Among these dioctyl sulfosuccinate ionic liquids, the ionic liquids with quaternary phosphonium as cation exhibit much better thermal stability than the others. It can be seen from the corrosion tests that both the synthesized ionic liquids and the reference sample corrode the magnesium alloy to some extent, which may be attributed to the high activity of magnesium alloy and the high polarity of the ionic liquids. However, the dioctyl sulfosuccinate ionic liquids corrode the magnesium alloys surface much lighter than LF-104. 　Among the dioctyl sulfosuccinate ionic liquids containing the same alkyl chain, alkylimidazolium corrode the surface most heavily, while quaternary ammonium salts and quaternary phosphonium salts corrode the surface lighter. The increase of the alkyl chain length in the ionic liquids aggravates the corrosiveness of the ionic liquid to the magnesium alloy. QCM test results indicate that the dioctyl sulfosuccinate ionic liquids have higher adsorption mass on the surface of magnesium alloy, compared to the reference sample L - F104. When being used as lubricants for steel/magnesium alloy, the synthesized dioctyl sulfosuccinate ionic liquids exhibit lower and more stable friction coefficients and much smaller wear volumes than the reference sample L-F104. Among the dioctyl sulfosuccinate ionic liquids, the anti-wear performance of ionic liquids with quaternary phosphonium cation is better than that of quaternary ammonium salt ionic liquids, while alkylimidazolium ionic liquid exhibit the worst anti-wear performance, which is basically consistent with the corrosion results. In addition, increasing the alkyl chain of cations can significantly improve the anti-wear performance of the ionic liquids. Furthermore, the tribological performances under different loads show that the dioctyl sulfosuccinate ionic liquids exhibit excellent lubricating performance as lubricants for magnesium alloy under different loads. 　The contact resistance was also collected during the friction tests, which can reflect the thickness and stability of the lubricating film forming between the lubricant and the friction pair surface during the friction tests. The contact resistances of the synthesized ionic liquids are higher than that of the L-F104, and they can be kept in a high range during the friction test, which indicates that the synthesized ionic liquid can form an effective protective film on the surface during the friction process to achieve better anti-friction and anti-wear effect. According to the SEM morphologies of the worn surface lubricated by different lubricants, the wear of the magnesium alloy surfaces are mainly abrasive wear and corrosion wear under the lubrication of these lubricants. From the XPS results, it can be seen that the formed tribochemical reaction film are similar for the different ionic liquids, which contains MgSO₄, MgO and other substances. There is no significant peaks of N element and P element before and after friction, which indicates that the tribochemical reaction occurs mainly between the anions and the surface of magnesium alloy during the friction process. The tribochemical reaction film can prevent the direct contact between the metal surfaces during the friction process, thereby achieving the anti-friction and anti-wear effect. Both the adsorption film and tribochemical reaction film determine the lubrication performance of the ionic liquids to magnesium alloy.