Abstract:In order to define allelopathic effects of volatile from Trifolium repens L., the influence of volatile from T.repens flowers and leaves on seed germination and seedling growth of Echinochloa crusgalli (L.) Beauv. and Abutilon theophrasti Medic. were tested with Petri dish bioassay, and the chemical components of the volatile were analyzed using GC-MS. The results indicated that the inhibition effect of flowers volatile stronger than that of leaves volatile, the allelopathic effect index of germination rate and shoot length of A.theophrasti were -0.27 and -0.29, the allelopathic effect index of the root length and fresh weight of E.crusgalli were -0.30 and -0.28. Twenty-three components were identified in volatile from T.repens flowers, the main components were 4-methyl-1, 3-pentadiene and cis-3-hexenyl acetate; and 24 components were identified in volatile from T.repens leaves, the main components were ethyl vinyl ether, cis-3-hexenyl acetate and acetone. The volatile from T.repens have allelopathic effects to E.crusgalli and A.theophrasti, components of volatile from T.repens mainly obtained olefins and esters.