In the present study, the antioxidant activities and total secondary metabolite amounts of different extracts (methanol, acetone, and water) obtained from the leaf and flower parts of Onopordum bracteatum, which was collected from Muğla (Türkiye) were determined for the first time. Antioxidant activity studies were performed with DPPH, ABTS, β-Carotene/linoleic acid, FRAP, and CUPRAC methods. Secondary metabolite assays were carried out in order to determine the total phenolic, total flavonoid, and total tannin contents of the extracts. In addition, the toxicities (Brine shrimp) of water extracts and the anthelmintic effects of methanol and water extracts were investigated. The leaf methanol extract of O. bracteatum with the highest antioxidant activity in all tests, except the FRAP test (DPPH: IC50= 0.26 ± 0.01 mg/mL, ABTS: IC50= 0.19 ± 0.003 mg/mL, β-Carotene/linoleic acid: 72.98 ± 1.31%, CUPRAC: 34.02 ± 1.87 mg TE/g extract, FRAP: 3.96 ± 0.65 mg TE/g extract) used to determine the antioxidant activity was observed to have the highest total phenolic content (5.78 ± 0.24 mg GAE/g extract). The highest total flavonoid (32.17 ± 0.82 mg QE/g extract) and total tannin contents (16.41 ± 1.30 mg CE/g extract) were determined in leaf acetone and flower acetone extracts of O. bracteatum, respectively. Concerning the cytotoxic properties, concentration-dependent activity was seen in O. bracteatum water extracts against brine shrimp. Methanol extracts of O. bracteatum showed better anthelmintic activity than water extracts. The results will provide basic data for studies on the pharmacological and medical use of O. bracteatum.