The lack of petroleum reserves is a concern for researchers that encourage the development of plant-based alternative fuels. Supported by extensive palm oil in Indonesia so that palm oil has great potential to be used as raw material for making palm oil biodiesel. One disadvantage of biodiesel is its oxidation instability. Stability is one of the main concerns of fuel. The stability of biodiesel is lower compared to diesel fuel in general. However, the oxidation stability of biodiesel in terms of induction period (IP) can be enhanced by the addition of antioxidant additives. Antioxidants has a function to increase the induction period by donating hydrogen atoms to pro-oxidant molecules in oxidation reactions. Combination of two or more antioxidants to produce high antioxidation activity compared to a single type of antioxidant is called synergism. Combination of two antioxidants produces two interaction schemes; the donation of hydrogen from the more active antioxidants to regenerate other antioxidants, and the formation of heterodimers from the antioxidant molecules and as a result of autoxidation process. In this case, Tert-butylhydroquinone (TBHQ) and Butylated Hydroxytoluene (BHT) were used. Synergism is conducted by determining IP of each lone and combined antioxidant with the ratio 1:1, 1:3 and 3:1. The outcome shows TBHQ:BHT 3:1 has the best synergism than the others with the induction period value of 24.19 hours. FTIR result shows the appearance of wavenumber between 1150-1050 cm-1 representing ether functional group as a result of combination between the two different antioxidants. LCMS shows great result either with the satisfying yield with molar masses found 385 g/mol for the new formed compound. It sums up that the ratio of TBHQ:BHT 3:1 gives positive result. This implies that binary antioxidant has given synergism effect with an accurate ratio, thus it will be economically significant for the use of biodiesel.