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This research was undertaken to investigate the effect of gamma rays at dose rates of 5.0, 10.0 and 15.0 kGy on the chemical composition of essential oils, total antioxidants, total flavonoids and total phenols, as well as the antioxidant activity and the thiobarbituric acid (TBA) and the free radical-scavenging activity (DPPH) of thyme. Radiation processing increased the total phenols, total flavonoids and total antioxidants of thyme, and moderate changes were detected at doses of 5 and 10 kGy for the essential oils. Thymol was sensitive to irradiation, especially at 15.0 kGy doses. In addition, the evaluation of antioxidant activity using DPPH radical-scavenging activity indicated some decreases of antioxidant activity in irradiated samples, while thyme exposed to doses of 10 and 15 kGy exhibited a significant increase in TBA values. The irradiation process can facilitate the utilisation of thyme as a preservative ingredient in the food and pharmaceutical industry.