Abstract: 
Hypericum tomentosum (H. tomentosum) is a medicinal plant distributed in Mediterranean region, it’s commonly used in folk medicine for different health problems. Thus, this study aimed to investigate the antioxidant properties of aqueous extract of leaves of H. tomentosum.  The aqueous extract was obtained by boiling H. tomentosum leaves in distilled water. The total phenolics and flavonoids content were determined using folin-ciocalteu’s reagent and aluminum chloride, respectively. The aqueous extract of H.tomentosum was tested for antioxidant activity as determined by DPPH^• radical and hydrogen peroxide scavenging assays, reducing power assay, ferrous ion chelating and the ability of this extract to prevent hemolysis were also performed.  The result showed that aqueous extract of H.tomentosum possess high levels of polyphenols (303.10 ± 5.14 µg GAE/mg extract) and flavonoids (53.56 ± 1.74 µg QE/ mg extract). H .tomentosum exerted a powerful scavenging activity against DPPH^• radical and hydrogen peroxide with EC₅₀ values of 9.32 ± 0.96 µg/mL and 3.13 ± 0.49 µg/mL, respectively. Moreover, it exerted a powerful reducing ability and inhibits ferrous ion chelating .The extract exhibited a significant protective effect against AAPH-induced erythrocytes hemolysis. This study suggests that H.tomentosum may represent a prospective source of natural antioxidants to prevent and /or to treat oxidative stress related diseases.

Keywords: Antioxidant, Hypericum tomentosum, Oxidative Stress, Polyophenols, Flavonoids.