This study was carried out to explore herbicidal potential of an Ageratum conyzoides, a weed of family Asteraceae, against an exotic noxious weed parthenium (Parthenium hysterophorus L.). Different concentrations (0, 2, 4, 6, 8 and 10%) of aqueous extracts of various parts of the tested weed were used in laboratory bioassays. ANOVA revealed the significant effect of plant part bioassay and extract concentration on germination as well as various root and shoot growth parameters. Leaf extract was found as the most herbicidal where a 10% extract completely inhibited the germination and growth of parthenium. Root and inflorescence extracts were also highly inhibitory in suppressing the germination up to 89% and 95%, shoot length up to 80% and 89%, root length up to 86% and 91%, and plant biomass up to 89% and 98%, respectively. Stem extract showed the least herbicidal activity causing up to 46%, 59%, 73% and 37% reduction in germination, shoot length, root length and plant biomass, respectively. This study concludes that leaf, root and inflorescence extracts of A. conyzoides possess strong herbicidal potential against germination and growth of parthenium.