The chemical constituents of fistular onion stalk obtained by supercritical CO(2) extraction were separated and purified by silica gel and sephadex LH-20 gel column chromatography and the preparative TLC method and four flavonoids were obtained. On the basis of the spectral data, they were structurally identified as (+)-catechin, (-)-epicatechin, astragalin, and 3-O-beta-D(2-O-beta-D-glucopyranosyl)-glucopyranosides of kaempferol.