Minor constituents of the essential oil of Cyperus rotundus have been investigated. The three new sesquiterpene hydrocarbons (-)-isorotundene, (-)-cypera-2,4(15)-diene, (-)-norrotundene and the ketone (+)-cyperadione were isolated and their structures elucidated. The absolute configuration of (-)-rotundene was derived by chemical correlation and enantioselective gas chromatography.