For the purpose of studying the effect of denaturated lipid and tocopherol on mitochondrial oxidation system, the following experiments were carried out. The increase of TBA value during incubation of rat liver 9, 000×g supernatant was depressed by prior addition of tocopherol. The TBA value of supernatant originated from starved rat was higher than that from normal rat, and was also depressed by the addition of tocopherol. The relationship between peroxide value and TBA value during incubation of lipid from Torulopsis utilis was tested and the parallelism between them was comfirmed. The succinate ubiquinone reducing activity of acetone treated mitochondria was restored by the addition of Torula lipid. Ageing of Torula lipid in ethanol increased TBA value and lost the ability of Torula lipid to restore the succinate ubiquinone reducing activity. Torula lipid which was protected from the increase of TBA value by the addition of tocopherol preserved the ability to restore the enzyme activity for long time comparatively.