The antioxidant activities of dl-α-tocopherol (α-T), d-γ-tocopherol (γ-T), and d-δ-tocopherol (δ-T) were determined in methyl linoleate free from natural antioxidants and metals. The relative antioxidant activities of tocopherols, at the equivalent mole concentration, were in the order α-<γ<δ-T as generally recognized. In this study, the parts of tocopherols effectively used as antioxidants were merely 13% for α-T, 46% for γ-T, and 77% for δ-T. Tocopherols added to methyl linoleate were absolutely consumed during the induction period, and the consumption rate was in the order α-> γ->δ-T. The rate of the formation of tocopheroxyl radicals was in the order α->γ->δ-T. In the experiments oxidizing tocopherols by PbO₂, etc., the mobility of hydroxyl hydrogen of tocopherols and the stability of tocopheroxyl radicals were in the order α-> γ->δ-T. These data showed that the ability as hydrogen donors was in the order α->γ->δ-T. However, tocopherols were consumed by direct air oxidation in the order α-> γ->δ-T. These results suggest that superior hydrogen donors are not always excellent antioxidants. Because, the substituent effect of antioxidants, as shown in tocopherols, can increase not only the ability of antioxidant as hydrogen donor but also the unstability of antioxidant against air.