Antioxidant properties of lignin in edible oils such as arachide oil have been investigated. Reaction kinetics were measured by differential scanning calorimetry (DSC) and experiments entailed heating the pure oil or oil to which substances suspected of inhibiting oxidation, i.e. lignin or its fractions, had been added, with subsequent comparison of the thermograms obtained. Similar experiments were carried out for arachide oil with addition of the well known inhibitor 2,6-di-tert-butyl-4-methylphenol (BHT). Measurements described in this report prove that lignin and its fractions can be regarded as inhibitors in free radical auto-oxidation.