The chemical composition of the volatile oil from aerial parts of Hypericum triquetrifolium Turra was studied by GC-MS. Fifty components (97.1% of the total composition) were detected in the volatile oil. Germacrene-D (21.7%), β-caryophyllene (18.3%), δ-cadinene (6.4%), trans-β-farnesene (4.3%), α-humulene (3.8%), β-selinene (3.7%), γ-cadinene (3.3%) and trans-phytol (3.2%) were found to be the major constituents of the oil. The oil of H. triquetrifolium consisted of five monoterpene hydrocarbons (3.4%), two oxygenated monoterpenes (0.4%), twenty-two sesquiterpene hydrocarbons (77.1%), eight oxygenated sesquiterpenes (7.9%) and one oxygenated diterpene (3.2%). Twelve nonterpenic compounds were also consisted 5.1% of the oil. In conclusion, the oil of H. triquetrifolium was characterized by a high content of sesquiterpenes (85.0%), whereas monoterpenes contained only 3.8% of the essential oil.