Esters of thiolated Butylated hydroxytoluene (AO1 and AO2), bearing two antioxidant moieties (BHT and thioether), are synthesized and reported first time as competitive antioxidants for synthetic ester-based lubricant oil (trimethylolpropane trioleate, TMPTO). Differential Scanning Calorimetry (DSC) and Rotary Bomb Oxidation Test (RBOT) are utilized for the evaluation of Oxidation stability. Thermogravimetric Analysis (TGA) is performed for the thermal stability assessment. The synthesized esters have shown very promising results in all experiments such as 3 wt.% AO1 blended TMPTO has shown 15.3 and 4.4 times better oxidation stability in comparison with BHT and Irganox 1076 respectively in DSC. Again, isothermal TGA has shown that 1.5 wt.% AO1 blended TMPTO is 1.5 times better than BHT at reducing weight loss of TMPTO occurred by the oxidation process. Apparently, these compounds have given high oxidation stability to synthetic ester-based lube oil (TMPTO) by protecting from premature oxidative degradation.