A new flavonoid was isolated from the whole plant of Spiranthes australis (R. Brown) Lindl (Orchidacea). Its structure was characterized as 3,7-dimethoxy-5-hydroxy-2-([4-(3-methyl-2-butenyl)oxy]phenyl)-4H-1-benzopyran-4-one on the basis of chemical and spectral evidence including 2D NMR analysis.