The tree-of-heaven plant, due to the content of secondary metabolites with a variety of unique properties, is widely studied as a potential raw material for obtaining remedies for organic farming. Our work aimed to study the allelopathic effect of Ailanthus altissima extracts on tomato (Lycopersicon esculentum) seeds. Dry plant materials of ailanthus (leaves and seeds) were extracted with distilled water and applied to tomato seeds at a concentration of 15, 10, and 5 mg.ml^-1 of dry residue to investigate their impact on the energy of germination, total germination, length of radicles and hypocotyls. The result revealed that the ailanthus extracts from leaves, collected in June, and from seeds, collected from July, had a significant inhibitory effect on all studied parameters. The total germination rate of seeds was suppressed on average by 56.2–69.0% compared to the control, and by 44.2–57.0% compared to the chemical standard. The length of the tomato radicles decreased by 1.4–18.6 times compared to the control. The most significant decrease was observed in germination energy and hypocotyl length. All three ailanthus extracts tested in the concentration of 15 mg.ml^-1 significantly inhibited germination energy and hypocotyl growth of tomato seeds. It was concluded that the leaves and immature seeds of Ailanthus altissima contain potential allelopathic substances that affect the energy of germination, and total germination rate, and inhibit the hypocotyl and radicle length of tomatoes. Therefore, aqueous extracts of ailanthus should be used to protect tomato fields from weeds only in the post-emergence period.