Medicinal plants have varying natural products and several antioxidants. Antioxidants play a principal function to protect against destruction caused by oxidative stress (OS), <i>Rheum emodi</i> is not an exception, in which it is reported to have compounds that possess antioxidant activity, like polyphenolic compounds. In addition to that, other compounds have proven to have antidiabetic, antimicrobial, antifungal, cytotoxic, hepatoprotective, and nephroprotective activities. This study aimed to quantify the water extract of a powdered plant of <i>R. emodi</i> to evaluate its ability to scavage free radicals. Total phenolic, total flavonoid contents, and reducing ability were measured to consider possible sources of future novel antioxidants in plants. The TPC, TFC, and reducing power assay increased with increasing concentrations of <i>R. emodi</i>. At 1000 µg/ml, the absorbance ranged from 1.437 for TPC, 1.602 for TFC, and 1.638 for reducing power assay, which is more than the absorbance of the standards at the same concentration. The extracted content of reducing power, phenolic, and flavonoid compounds were higher than the standard pyrogallol, quercetin, and ascorbic acid.

Keywords: Adiantum capillus veneris Linn; Antioxidant; Reducing Power; Flavonoids; Phenolic Adiantum capillus veneris linn is a member of Adiantaceae family which has been used as a folk medicine in management of hyperglycemia. Although there are some reports showing that the aqueous extract of the plant is effective as hypoglycemic agent but there were no scientific reports for its effectiveness.In a biological system, an antioxidant can be defined as "any substance that when present at low concentrations compared to that of an oxidizable substrate would significantly delay or prevent oxidation of that substrate" [8].Antioxidants could protect the human body against free radicals that may cause pathological conditions, such as anaemia, arthritis, inflammation, neurodegeneration, aging process and per-The powdered dried leaves of A. capillus veneris L. was extracted continuously by Soxhelt extractor, five extracts (water, methanol, chloroform, ethyl acetate and acetone) were obtained and evaporated to dryness by rotatory evaporator. The extracts were investigated for antioxidant activity, reducing power and the presence of phenolic and flavonoid compounds.The antioxidant activity of A. capillus veneris L. was confirmed for all extracts with the highest activity for the water extract IC 50 = 2.7, this assay was also supported with reducing power assay, in which both methanolic extract and water extract exhibited the highest reducing power assay, while the ethyl acetate extract shows the highest total flavonoids content. The highest total phenolic content value was recorded for methanolic extract.