To evaluate the allelopathic effect of essential oil extracted from leaves of Eucalyptus globules against some certain weeds and the possibility of that being employed in weed management strategies, laboratory and greenhouse studies were conducted in Islamic Azad University of Khoy in 2007 in the framework of a factorial expreiment based on a randomized complete block design of four replications. The studied factors consisted of Eucalyptus essence concentrations of: 0.5, 2, 3.5 and 5 nl/ml in laboratory along with 0.25, 0.5, 0.75, and 1 v/v in pots with weeds including: Amaranthus retloflexus and convolvulus arvensis. Distilled water was used as control. Results indicated that germination percentage, germination rate, radicle length, plumule length, primary root length, primary pedicle length, seedling and plantlet lengths decreased, with increase in of essence concentrations. The highest allelopathic effect of the essential oil was observed against A.retloflexus. Plantlet length in A.retloflexus decreased from 39 mm to 9 mm in control, and as affected by the highest concentration of Eucalyptus essential oil application. Therefore, it can be concluded that Eucalyptus essential oil can be further studied, as a biological herbicide in the management and control of the above mentioned weeds.