Cousinia pterocaulos (C.A. Mey.) Rech. f., is an endemic species of the Asteraceae family in Iran and Transcaucasia, which is naturally distributed in northern regions of Iran. In the current study, we evaluated the composition of essential oil, total flavonoids and phenolic compounds, and free radical scavenging activity of C. pterocaulos extract. Plant materials were collected from a natural population of C. pterocaulos in Mazandaran, and identified based on description provided in Flora Iranica. Essential oil from aerial parts of this plant was extracted using Cleavinger type apparatus and analyzed its composition using GC and GC/MS apparatus. Moreover, the methanolic extracts from aerial parts were used to determine its total flavonoid and phenolic compounds and also capacity in scavenging the stable DPPH free radicals. The results indicated that total phenolic and flavonoids contents in this species is relatively small compared with other Cousinia species. Meanwhile, its capacity in scavenging free radicals is relatively higher than other species that were reported in previous studies. Furthermore, the main essential oil composition was 4,6-Heptadiyn-3-one (43.8%), which has not been detected in other Cousinia species. These findings revealed that each Cousinia species has a specific phytochemical property, leading to a unique biological activity.
