A new potential allelochemical A,m.f. C33H40O20, [M+] 756, mp.228-2310C has been isolated from ethanolic extract of the stems of Bidens biternata(Lour.) Merrill &Sherff. Along with two known compounds B and C. The structure of the compound A was characterized as 5, 7, 8, 4' tetra hydroxy 3, 5' di-methoxy flavone- 7-O-α-Lrahmnopranosyl- 4'-O-β-D-arabinopyranosyl(1→4)-O-β-D-xylopyranoside by various colour reactions, spectral analysis and chemical degradations.