In this study, we report isolation of flavonoids, viz., 3-O-methylquercetin, tangeritin, luteolin-7-O-glucoside, luteolin, apigenin-7-O-glucoside, apigenin-8-C-glucoside, luteolin-8-C-glucoside, luteolin-6-C-glucoside, diosmetin and catechin from the methanolic extract of Hyparrhenia hirta employing high performance liquid chromatography and liquid chromatography-electrospray ionization-tandem mass spectrometry. The total phenolic content of H. hirta extract was 105.58 ± 0.1 mg gallic acid equivalents/g of plant extract while the total flavonoid content was 45.20 ± 0.2 mg quercetin equivalents/g of plant extract and the total condensed tannin were 72.35 ± 0.7 mg catechin equivalents/g of plant extract by reference to standard curve. The antioxidant activity was assayed through the antioxidant capacity by phosphomolybdenum assay, the reducing power assay and the radical scavenging activity using 2,2-diphenyl-1-picrylhydrazyl method. The extract showed dose dependant activity in all the three assays.
