The aim of the present study was to investigate the antioxidant activities of 11 phenolic compounds pre-viously isolated from an endemic Centaurea ensiformis P.H. Davis (Asteraceae) by 2,2-diphenyl-l-picryl-hydrazyl (DPPH) and ABTS decolorization assays. These compounds consisting of 2 phenolic glycosides (tacioside and protocatechuic acid), 2 acetophenon glycosides (picein and 4-hydroxyacetophenon 4-0-[6’-0-P-D-apiofuranosyl]-P-D-glucopyranoside). 1 coumarin glucoside (scopolin), 4 flavonoid glycosides (vicenin-2, schaftoside, neoschaftoside and clnysoeriol-7-O-mtinoside), 1 phenylpropanoid glycoside (sy-ringin) and 1 neolignan glucoside (dihydrodehydrodiconiferyl alcohol 4-O-P-D-glucopyranoside). Protocatechuic acid and tachioside had the highest activity (DPPH IC50: 6.47 and 22.87 inM; TEAC: 33.2+0.18 and 31.2±0.99, respectively) in both methods. Dihydrodehydrodiconiferyl alcohol 4-O-P-D-glucopyranoside also showed liigh activity compared to ascorbic acid in DPPH assay (IC50: 27.7 inM). Our results concluded that the C. ensiformis liave a potential source of antioxidants of natural origin