Open AccessThe aim of this work was to investigate the total phenolic content and antioxidant potential of aqueous extract of Phyllanthus amarus. The aqueous extract of Phyllanthus amarus whole plant was prepared then systematically investigated by various antioxidant assays, including: DPPH- (1, 1-diphenyl-2-picrylhydrazyl radical), Nitric oxide radical inhibition activity, and β–carotene-linoleate method, compared with ascorbic acid and rutin. Its total phenolic content was also measured by Folin-Ciocalteu colorimetric method. P. amarus aqueous extract exhibited effective antioxidant activity in dose-dependent manners and its IC50 values were calculated as 4.21±0.379, 426±0.512, 126±0.348 for DPPH, Nitric oxide radical inhibition activity, and β–carotene-linoleate assay respectively. Its total phenolic content was 52.71± 0.214 mg GAE /g. P. amarus aqueous extract has effective in vitro antioxidant activity which may attribute to its total phenolics, among which phyllanthin and hypophyllanthin can be considered as the active components. The pharmacological effects or healthcare functions of P. amarus may result from the synergistic effects caused by the combination of its components and its antioxidant effect plays an important role in the synergistic effects.