In nature, plants show an allelopathic effect on other plants it may be inhibitory or stimulatory. In our experiment, we study the allelopathic effect of various parts of Parthenium hysterophorus L. on germination and seedling growth of Triticum aestivum L. Under well-sterilized conditions, we prepared an aqueous extract of root, stem, and leaves of Parthenium hysterophorus L. at various concentrations (0%, 5%, 10%, 15%, and 20%). After the effect of root extract, stem extract, and leaves extract on Triticum aestivum L. we measured germination percentage, shoot length, root length, wet biomass, and dry biomass. The stem extract and root extract have no significant effect on germination percentage. But leaves extract shows an inhibitory effect on germination percentage. The leaf extract of Parthenium hysterophorus L. shows an inhibitory response on shoot length at all concentrations and the root extract of parthenium shows a stimulatory response on shoot length at all concentrations. Leaves extract of Parthenium hysterophorus L. shows a high inhibitory effect on shoot length, root length, germination rate, and wet biomass of Triticum aestivum L, the root length of Triticum aestivum L. is strongly inhibited than shoot length. It’s may because secondary metabolites present in leaf extract inhibit gibberellin and indoleacetic acid function (Tefera T. 2002). The release of allelochemicals from leaves extract of parthenium in low amounts stimulates growth, while greater amounts result in inhibition of other plants (Hassan G. et al., 2018).