As phenolic polymer compound, the hydroxyphenolic groups in lignin enable it to act as antioxidant. In this study, organosolv and commercial lignin were tested for their activity as antioxidant in biodiesel. Organosolv lignin was obtained by first performing pretreatment of Oil Palm Empty Fruit Bunch (OPEFB) by organosolv method at 170°C for 2.5 hours followed with isolation by use of H2SO4 20%. The organosolv and commercial lignin were added separately to biodiesel with concentration variation of 500, 1000, and 1500 ppm. Synthetic antioxidant butylated hydroxytoluene (BHT) was used as positive control in this study. Biodiesel oxidation stability test was performed by Rancimat method. Antioxidant activity tests were done by determining the acid value, peroxide value, and kinematic viscosity of biodiesel each week for 4 weeks. The yield and lignin content of organosolv lignin obtained from this study were 13,7% and 64.5% respectively. Hydroxyphenolic content of organosolv lignin by means of spectroscopy method showed value of 6.8%. Addition of organosolv lignin, commercial lignin, or BHT showed ability to inhibit the oxidation rate of biodiesel with the sequence of antioxidant activity from the largest to the smallest are successively BHT, commercial lignin, and organosolv lignin. Rancimat test showed that 1500 ppm organosolv lignin resulted 4.2 minutes biodiesel induction time which equals the result of 1000 ppm commercial lignin as well as 500 ppm BHT. This study reveals that organosolv lignin from OPEFB and commercial lignin have future potential to be utilized as natural antioxidant for biodiesel.