Phenolic compounds are widely recognized because of their antioxidant capacity. In the present work, caffeic add was shown to minimize the formation of oxidative radicals in soybean biodiesel, according to the induction period (IP) obtained by the Rancimat method. Its efficiency was much higher than usual antioxidants, such as butylated hydroxytoluene (BHT) and tert-butylhydroquinone (TBHQ). With a decomposition temperature of 170 degrees C, caffeic add retained its properties, showing excellent antioxidant activity even when subjected to accelerated oxidation tests. While contamination with metals led to a meaningful decrease of the oxidative stability of soybean biodiesel, when small amounts of caffeic acid (500 mg L-1) were also present in the fuel, IF values higher than 6 h were obtained, reaching the limit specified by EN 14214.