A quaternary ammonium salt of isooctylthiophosphate (MDAPD) was synthesized. The tribological properties of MDAPD in three different base oils (synthetic oil, rapeseed oil, mineral oil) were evaluated by fourball tester, and its fluidity，thermal stability and corrosivity were also measured. The worn surface morphology and chemical composition were analyzed by SEM and XPS separately. The results indicate that the synthesized MDAPD has good thermal stability, excellent fluidity at low temperature and good corrosion resistance in these base oils. MDAPD has good wear resistance in synthetic and rapeseed oil. The surface analysis reveals that the formation of FeSO4, Fe2(SO4)3, FeS, FeS2 and FePO4 in the boundary film enhances antiwear properties of the base oil.