Acroptilon repese (L.) Dc (Asteraceae) is a perennial herb with erect stems growing to 80 cm in height. It is a wide distributed plant that is native to Magnolia, Western Turkistan, Iran, Turkey and captain Asia and was introduced into America and Canada at the beginning of previous centaury. In the present work we study the chemical composition of the aerial parts of the plant and phytotoxic effects of the oil against some weeds. The hydrodistillated essential oil from aerial parts of A. repens was analyzed by GC-MS. Totally 26 compound were identified. Main components of the oil are: Caryophyllen oxide (9.6 %), beta-cubebene (9.5 %), beta-Caeyophyllen (9.2 %) alpha-copaen (8.7 %). The results of phytotoxic assay indicated that the essential oil obtained from Acroption repens significantly reduced seed germination of Amaranthus retroflexus and Cardaria draba, two common weed, in a dose dependent manner. On the other hand, the essential oil of A. repens inhibited significantly the root growth of A. retroflexus and C. draba seedlings. The oil strongly reduced the shoot growth of A. retroflexus seedlings, as well as.