In this study, the effect of gamma irradiation on the total phenolic content and antioxidant activity of Satureja hortensis, Thymus vulgaris, and Thymbra spicata was evaluated. Plants irradiated in a 60Co irradiator to 0, 1.2, 3.0, and 5.1 kGy at 25 degrees C. Control and irradiated samples were extracted with methanol. The antioxidant activity of methanol extracts was determined using phosphomolybdenum assay and the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging method. The total phenolic content in three spices was found to decrease with irradiation except at 5.1 kGy for S. hortensis. The DPPH radical scavenging activity of the extracts decreased after irradiation.