The allelopathic effects of fresh shoot aqueous extract of Tithonia diversifolia (Hemsl.) A.Gray, an invasive species introduced into Africa from North and Central America, on the growth of seedlings of three woody species: Monodora tenuifolia, Dialium guineense and Hildegardia barteri were investigated. The fresh shoot aqueous extract of Tithonia diversifolia was applied to the established seedlings of the three woody species over a period of ten weeks. The fresh shoot aqueous extract of Tithonia diversifolia had a significant effect (inhibitory and stimulatory) on growth parameters such as shoot height, leaf area, number of leaves and chlorophyll content of the three woody species. The study revealed that the fresh shoot aqueous extract of Tithonia diversofolia have different effects (inhibitory and stimulatory) on the seedlings and the mode of action depends on the associated woody plant species.