The effect on induction period and tocopherol content after gamma-irradiation on samples of olive oil and seed oils ( sunflower and soybean) was determined. In seed oil samples 0, 100, 200 and 300 ppm of delta-tocopherol were added before irradiation with 1, 2 and 3kGy. The results of induction period showed that, after irradiation, all samples presented a significant decreased in resistance to oxidation. However, this decrease was minimized when delta-tocopherol was added. Irradiation significantly decreased the level of tocopherols. delta-Tocopherol appeared more sensitive in irradiation process than alpha- and gamma-tocopherol. The addition of delta-tocopherol significantly reduced, in most cases, the depletion of the other tocopherols.