Objective: To evaluate the phytochemical and in vitro antioxidant ability of methanolic extract and different fractions of Amaranthus graecizans subsp. silvestris (A. graecizans subsp. silvestris). Methods: Methanolic extract of A. graecizans subsp. silvestris was obtained by cold maceration and then methanolic extract was subjected to fractionation and different fractions i.e. n-hexane, chloroform, ethyl acetate, n-butanol and aqueous fractions were obtained. Methanolic extract and all other fractions were subjected to phytochemical investigation by performing different phytochemical group tests like alkaloid, tannins, carbohydrates, lipids, proteins, etc. In vitro antioxidant activity of A. graecizans subsp. silvestris was evaluated by using 1, 1-diphenyl-2-picrylhydrazyl radical (DPPH), ferric thiocyanate assay, total antioxidant activity by phosphomolybdenum, ferric reducing antioxidant power, total phenolic content and lipid peroxidation methods. Results: Maximum antioxidant activity was shown by n-hexane fraction of the extract by carrying out DPPH (86.44±0.23), ethyl acetate fraction by total antioxidant (0.95±0.06) and ferric reducing antioxidant power (299.45±1.48) methods, while by employing total phenolic contents and inhibition of lipid per oxidation assays, methanolic extract (92.88±4.16) and n-hexane fraction (69.47±0.68) exhibited maximal activity. Ethyl acetate fraction showed the least IC