Differential scanning calorimetry (DSC) was employed to evaluate the performance of an eater lubricant containing sodium stearate. In the isothermal DSC oxidation test, sodium stearate is an effective synergist for arylamine antioxidants such as p,p’-dioctyldiphenylamine (DODPA). When combined with arylamine antioxidants, sodium stearate can also effectively reduce the increases in viscosity and acid number of the ester oil in oxidation-corrosion tests. The electron paramagnetic resonance (EPR) results indicated that sodium stearate can reduce the free radical contents in the oxidized oil in the presence of arylamine antioxidants.