This study investigated the chemical composition of Cirsium japonicum var. ussurience Kitamura essential oil and the quantitative changes of major volatile flavor compounds according to the harvesting season. The essential oils obtained by the method of hydrodistillation extraction from aerial parts of C. japonicum var. ussurience Kitamura were analyzed by GC and GC-MS. Sixty-four volatile flavor compounds were identified in the essential oil from C. japonicum var. ussurience Kitamura harvested in May 2012; hexadecanoic acid (49.31%) was the most abundant compound, followed by 6,10,14- trimethyl-2-pentadecanone (13.72%), phytol (13.40%) and 9-hexadecenoic acid (4.16%). Eighty-three compounds were identified in the essential oil from the plant harvested in October 2012; phytol (40.56%), hexadecanoic acid (17.69%), 6,10,14- trimethyl-2-pentadecanone (13.71%), and caryophyllene oxide (4.15%) were the most abundant compounds. Types and levels of volatile compounds from different harvesting seasons varied. The essential oil composition of C. japonicum var. ussurience Kitamura harvested in the spring and autumn was characterized by higher contents of aliphatic fatty acid, diterpene and sesquiterpene, respectively.