The essential oils obtained by hydrodistillation of aerial part of Cyperus difformis L., and Cyperus arenarius Retz grown in Iran were analyzed by GC-MS. Analysis oils showed the predominance of sesquiterpenes compounds in addition to monoterpenes. Twenty-three components of C. arenarius and Twentynine components of C. difformis representing 87.8 % and 89.8 % of the oils were identified, respectively. Cyperene (21.9 %) and cyperotundone (12.5 %) were the major components of C. arenarius, whereas in the oil of C. difformis, cyperene (34.8 %), cyperotundone (7.8 %), isorotundene (7.8 %) were the main constituents. Both oils were richer in sesquiterpene hydrocarbons and oxygenated sesquiterpenes.