Ligularia virgaurea is a noxious weed widely distributed on the psychro-grasslands of east Qinghai-Tibet Plateau of China, but the allelopathic effects of its volatile is less known. In this study, the allelopathy of L. virgaurea volatile to 5 kinds of grasses was examined, and its chemical constituents were analyzed by GC-MS. The results demonstrated that the volatile of growing L. virgaurea could inhibit the seed germination speed and germination rate of all tested grasses. The inhibitory effects on Elymus nutans and Bromus magnus were significant, while Poa annua and Festuca ovin were not very sensitive. 18 major constituents were identified from the essential oil of L. virgaurea, accounted for 68.24% of the total. The main chemical components were 2-methylheptane (9.84%), 3-methyl-heptane (8.25%), heptane (7.93%), 4-methyl-1-(methylethyl)-bicyclo [3, 1, 0] hex-2-ene (7.79%), 3-methyl-hexane (6.38%), 2-methyl-hexane (5.54%), and D-limonene (4.70%). Monoterpenoids accounted for 16.58% of the total, indicating that volatilization was one of the ways by which L. virgaurea released allelochemicals. The allelopathy of the volatile may play an important role in enhancing the competitive ability of the species, and be one of reasons of grassland degeneration.