The purification of a MeOH extract from the rhizome of Acorus gramineus (Araceae) using column chromatography furnished two new stereoisomers of phenylpropanoid, acoraminol A (1) and acoraimol B (2). It also furnished 17 known phenolic compounds, β-asarone (3), asaraldehyde (4), isoacoramone (5), propioveratrone (6), (1'R,2'S)-1',2'-dihydroxyasarone (7), (1'S,2'S)-1',2'-dihydroxyasarone (8), 3',4'-dimethoxycinnamyl alcohol (9), 3',4',5'-trimethoxycinnamyl alcohol (10), kaempferol 3-methyl ether (11), 2-[4-(3-hydroxypropyl)-2-methoxyphenoxy]-1,3-propanediol (12), hydroxytyrosol (13), tyrosol (14), (2S,5S)-diveratryl-(3R,4S)-dimethyltetrahydrofuran (15), (7S,8R)-dihydrodehydrodiconiferyl alcohol (16), 7S,8S-threo-4,7,9,9'-tetrahydroxy-3,3'-dimethoxy-8-O-4'-neolignan (17), 7S,8R-erythro-4,7,9,9'-tetrahydroxy-3,3'-dimethoxy-8-O-4'-neolignan (18), and dihydroyashsbushiketol (19). The structures of the new compounds were elucidated by analysis of spectroscopic data including 1D and 2D NMR data. The absolute configurations of 1 and 2 were determined using the convenient Mosher ester procedure. Compounds 5-19 were isolated for the first time from this plant source. The isolated compounds were tested for cytotoxicity against four human tumor cell lines in vitro using a Sulforhodamine B (SRB) bioassay.