Phytotoxicity is the term used to describe the toxic effect of chemical compounds on growth and development of plants. Phytotoxic compounds vary in their chemical composition, and may be found in natural environments due to their biosynthesis and active release (allelochemicals). These compounds have the potential to be used as natural pesticides for the control of agricultural plagues. Therefore, this study aimed to evaluate the phytotoxic potential of different extracts and fractions of Tridax procumbens, using pre and post-emergence bioassays of Lactuca sativa L. seeds and mitotic index of Allium cepa L. root cells. Furthermore, the chemical compounds present in the extracts were phytochemically elucidated and the most bioactive fraction determined. Germination and development of tested seedlings were inhibited by the different extracts and ethyl acetate fraction of the ethanolic extract. There were notable alterations in the mitotic index of exposed A. cepa root cells compared to those of the negative control. Phytochemical identification was performed by HPLC-PAD, which showed that a considerable amount of flavonoid compounds were present in the ethanolic extract and its ethyl acetate fraction. According to the results obtained, it can be concluded that T. procumbens possesses phytotoxic compounds that are probably of flavonoid origin. The possession of these bioactive compounds may be related to its invasive nature and weed capacity.