The dynamics of initiation and inhibition of lipid peroxidation by α-tocopherol (α-Toc) in membranes were investigated under biological conditions using phosphatidylcholine liposomes. First, I examined how superoxide generated in the bulk water phase is able to induce lipid peroxidation in the inner hydrophobic region of the membrane. Second, I studied the localization of the antioxidant OH group of α-Toc in membranes and its lipid radical-trapping dynamics. Third, I investigated how α-Toc that is oxidized during radical trapping in membranes is recycled by ascorbic acid (AsA) in the bulk water phase. Finally, I studied the deactivation by α-Toc of singlet oxygen (¹O₂), which was generated by photoirradiation at the membrane surface, in the hydrophobic membrane inner region, and in bulk water, and measured the ¹O₂ deactivating rate constant of α-Toc in membranes considering: the concentration and mobility of α-Toc molecule in membranes, especially those of its active OH moiety located at the membrane domains, such as the membrane surface polar zone, inner hydrogen belt, and hydrophobic core, and the dielectric constant reflecting the reactivity of the OH moiety and ¹O₂ in the membrane domains where they interact.