MoS₂–polydopamine–methoxypolyethyleneglycol amine (MoS₂–PDA–MGA) was synthesized through the combination of mussel-inspired chemistry and the Michael addition reaction. The modification of MoS₂ via PDA and MGA enhanced its dispersion stability in oil. The tribological properties of MoS₂–PDA–MGA for use as additives in polyalkylene glycol (PAG) base oil were investigated using an oscillating reciprocating tribometer at elevated temperatures. The results indicated that the addition of 0.7 wt% MoS₂–PDA–MGA in PAG resulted in excellent friction-reducing and anti-wear (AW) performances compared with PAG base oil. The tribological results of MoS₂–PDA–MGA and MoS₂ dispersed in PAG base oil after settling for 7 days indicate that MoS₂–PDA–MGA, with its good dispersion stability, has stable friction-reducing and AW properties. XPS analysis suggested that a protective boundary film formed on the wear surfaces during the friction and wearing process, which was believed to be responsible for the excellent tribological performance of MoS₂–PDA–MGA dispersed in PAG at elevated temperature.