Metal-based room-temperature ionic liquid methyltri-n-octylammoniummolybdate ( [(CH3)N(n-C8H17)3]2MoO4 ) was synthesized with methyltri-n-octylammoniumchloride, sodium molybdate dihydrate and silver nitrate, and characterized by FT-IR, 1H NMR, API-ES-MS and elemental analysis, which have been extended to new families and generations of functionalized ILs. Its tribological performances as additive in base oil 400SN were examined on a four-ball tester. Adding 0.5% (mass concentration) molybdenum ionic liquid in base oil 400SN improved the PD value of base oil one lever, increased the PB value by 23.8% and dropped WSD by 34.6%. The tribofilm [(CH3)N(n-C8H17)3]2MoO4 generated on the worn surface was analyzed by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The results showed that [(CH3)N(n-C8H17)3]2MoO4 blend oil exhibited excellent anti-wear ability and extreme-pressure performance, which could be attributed to tribo-chemically boundary films formed on the rubbing surface consist of MoOx and FeOx.