10.22376/ijpbs.2019.10.1.p1-12 Volume 3 Issue 4 2012(October - December) A flavonoid compound was isolated from the methanolic extract of lessThan i greaterThan C.salignus lessThan /i greaterThan leaves and the structure was elucidated as 3′, 4′, 5, 7 Tetra Hydroxy Flavonol by UV, IR, NMR and Mass Spectra. This compound was isolated first time from this plant extract. In present study antioxidant capacities of the isolated compound was determined by two different assays, like DPPH radical scavenging activity method and Hydrogen Peroxide scavenging activity method. For both the models ascorbic acid was used as reference standard. Alterations of the absorbance due to free radicals were tested in control, test (isolated compound from lessThan i greaterThan C salignus lessThan /i greaterThan extract), & also standard (stock solution of ascorbic acid) groups. Our findings suggested that, isolated compound of lessThan i greaterThan C salignus lessThan /i greaterThan leaves possessed a very good antioxidant activity in dose dependant manner and also comparable with the reference standard one. S.CHOWDHURY , A.K.GHOSH , S.MAJI AND N.N.BALA Isolation, 3′, 4′, 5, 7 Tetra Hydroxy Flavonol, Anti-oxidant. 112-118