Biodiesel is composed of saturated and unsaturated long chain fatty acid alkyl esters. Due to these unsaturated compounds, there is a susceptibility to the autoxidation process. Castor biodiesel has excellent thermal and oxidative stabilities due to its chemical composition. Blends of sunflower and castor were obtained in the ratios 20, 40, 60 and 80% m/m with the intention to study the effect of the addition of castor biodiesel on the induction period of sunflower biodiesel of low oxidative stability, employing the Rancimat method (EN 14112) and P-DSC isothermal mode. The above mentioned blend containing 40% of castor biodiesel in sunflower biodiesel meets the specification of oxidative stability (6 hours). Furthermore, it was observed that the addition of castor biodiesel is interesting, since it improves the resistance to the oxidation of sunflower. The results obtained by Rancimat and P-DSC were consistent with respect to the analysis of biodiesel blends, indicating that the use of P-DSC technique to study the oxidative stability is quite promising2030-12