The rhizome of Acorus tatarinowii is a well-known traditional Chinese medicine. Our extensive investigation on this plant material afforded two new compounds, including a cadinane-type sesquiterpenoid and a pyrazine derivative, along with seven known compounds. The structures of the new compounds, tatarinowin B and tatarinine A, were elucidated as 2-oxocadinan-1(10),3-dien-5-ol (1) and 2-(3',4'-dihydroxy-1'-butylenyl)-5-(2'',3'',4''-trihydroxybutyl)-pyrazine (2), respectively, by means of spectral methods.