The antioxidant properties of some single components and the total antioxidant activity of extra-virgin olive oil have been evaluated by the oxygen radical absorbance capacity (ORAC) method. The total ORAC of the extra-virgin olive oil was found to be positively correlated with the concentration of total polyphenols, which are important to the shelf life of the product. Among the single phenolic compounds studied, gallic acid showed a higher ORAC than caffeic acid and oleuropein, while among the derivates of oleuropein, hydroxytyrosol was found to be the most active compound among all the phenols studied. The total ORAC of commercial olive oils differed according to the concentration of total polyphenols. The total ORAC of extra-virgin olive oil was constant during 1 year of storage in rational conditions, whereas it worsened dramatically in olive oil damaged by the lipase-producing yeast Williopsis californica or by lipase from Pseudomonas spp. The study accomplished on the oily fraction of the fruits before harvesting demonstrated that the total ORAC of the oil of under-ripe green olives is higher compared to that shown by mature fruits; therefore, through the choice of the harvesting time, it is possible to define also the future content of polyphenols of the oil. The total ORAC test, together with other analyses, can be considered as a qualitative parameter that can contribute to the expression of technological and health virtues of extra-virgin olive oil.