The rhizome and leaf essential oil compositions of Acorus calamus L. (Araceae) have been investigated in detail from various parts of the world, but the root oil composition has rarely been investigated. In present study, the root essential oil composition of A. calamus was investigated using gas chromatography (GC) and GC-mass spectrometry. A total of 21 constituents, forming 76.6 % of the total oil composition were identified. Major constituents of the oil were beta-gurjunene (28.0 %), (Z)-asarone (13.7 %), aristolene (13.4 %), and (E)-asarone (7.9 %). The root oil composition was quite different from rhizome and leaf oil compositions of A. calamus.