Acorus tatarinowii, a relative of Acorus calamus, was shown to contain the following compounds in the essential oil steam distilled from the root. Eighteen compounds were isolated from the rhizome of Acorus tatarinowii.Their structures were identified by spectroscopic data as(7S,8R)-4,9′-dihydroxyl-3,3′-dimethoxyl-7,8-dihydrobenzofuran-1′-propylneolignan(1),(7S,8R)-4,9′-dihydroxyl-3,3′-dimethoxyl-7,8-dihydrobenzofuran-1′-propylneoligan-9-O-β-D-glucopyranoside(2),7′-hydroxylariciresinol-9-acetate(3),5-hydroxy-3,7,4′-trimethoxyflavone(4),rhoifolin(5),astragalin(6),pinocembrin-7-O-rutinoside(7),kaempferol-3-O-rutinoside(8),rhodionin(9),isoschaftoside(10),5-hydroxymethyl-2-furaldehyde(11),trans-cinnamic acid(12),3,7-dihydroxy-11,15,23-trioxo-lanost-8,16-dien-26-oicacid(13),3,7-dihydroxy-11,15,23-trioxo-lanost-8,16-dien-26-oic acid methyl ester(14),cycloartenol(15),daucosterol(16),lupeol(17),(22E,24R)-ergosta-5,7,22-trien-3β-ol(18).Except for compounds 4,11,and 16,all the other substances were obtained from this plant for the first time.