Sideritis L. species are widely used as medicinal plants and as herbal teas in Turkey, in which 45 species of the genus are naturally found. The aim of this study was to determine the antioxidant activity of Sideritis species found in the Mediterranean region. In this study, the antioxidant activities of the lyophilized extracts obtained from aerial parts of 17 species (18 taxa) of Sideritis were compared, of which 15 taxa were endemic. The antioxidant activities of aqueous extracts were studied by two different techniques: qualitative DPPH (1,1-diphenyl-2-picrylhydrazyl radical) assay to detect the free radical scavenging activity and the TBA assay to detect liposome lipid peroxidation. All the extracts (except S. erithrantha subsp. erithrantha, S. dichotoma, S. syriaca subsp. nusariensis, S. tmolea) showed a strong antioxidant activity with the DPPH test. High activity was observed in the S. brevibracteata (IC50 mg/ml = 0.16), S. condensata (IC50 mg/ml = 0.33), S. serratifolia (IC50 mg/ml = 0.31) extracts with the lipid peroxidation assay method.